Study Guide Mathematics and Applied Mathematics Calculus WTW 114 © 2025 University of Pretoria 1 Contents Module Calendar: Important Dates & Overview 4 Course Details A Welcome . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 7 Welcome 7 B Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 C Assessment and related matters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 D Contact time and study hours . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 E Disciplinary issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 1 Functions 1.1 Logic/Proofs (2 lecture) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Numbers, intervals and inequalities (1 lecture) . . . . . . . . . . . . . . . . . . . . . . . 1.3 The absolute value (2 lectures) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4 Trigonometry (1 lecture) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5 Functions and their graphs (2 lectures) . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.6 New functions from old functions (2 lectures) . . . . . . . . . . . . . . . . . . . . . . . 16 16 16 19 20 23 25 2 Limits and Continuity 2.1 The tangent and velocity problems (1 lecture) . . . . . . . . . . . . . . . . . . . . . . . 2.2 The limit of a function (1 lecture) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 Limit laws (1 lecture) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4 Precise definition of a limit (1 lecture) . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5 Continuity (3 lectures) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6 Limits at infinity and horizontal asymptotes (1 lecture) . . . . . . . . . . . . . . . . . . 26 26 26 27 27 28 28 3 Differentiation 3.1 Derivatives and rates of change (1 lecture) . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 The derivative as a function (1 lecture) . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 Differentiation rules (2 lectures) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4 Derivatives of trigonometric functions (1 lecture) . . . . . . . . . . . . . . . . . . . . . 3.5 The chain rule (2 lectures) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6 Exponential functions and the number e (1 lecture) . . . . . . . . . . . . . . . . . . . . 3.7 The derivatives of inverse functions (2 lectures) . . . . . . . . . . . . . . . . . . . . . . 3.8 Implicit differentiation (1 lecture) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.9 Logarithmic functions and their derivatives (2 lectures) . . . . . . . . . . . . . . . . . . 3.10 Hyperbolic functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 29 30 31 33 34 35 38 44 45 49 2 4 Applications of Differentiation 4.1 Maximum and minimum values (2 lectures) . . . . . . . . . . . . . . . . . . . . . . . . 4.2 The Mean Value Theorem (2 lectures) . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 How the derivative affects the shape of the graph (2 lectures) . . . . . . . . . . . . . . . 4.4 Indeterminate forms and L’Hospital’s rule (2 lectures) . . . . . . . . . . . . . . . . . . . 4.5 Curve sketching (2 lectures) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6 Optimization problems (2 lectures) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.7 Antiderivatives (1 lecture) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 50 51 51 52 52 53 53 5 Integration 5.1 The area problem (1.5 lectures) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 The definite integral (2.5 lectures) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3 The Fundamental Theorem of Calculus (2 lectures) . . . . . . . . . . . . . . . . . . . . 5.4 Indefinite integrals (1 lecture) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5 Transformation of the integral (3 lectures) . . . . . . . . . . . . . . . . . . . . . . . . . 54 54 54 55 56 57 Appendices I Differentiation formulas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II Differentiation rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III List of standard indefinite integrals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 58 59 60 FLY@UP Support 62 Department’s Vision & Mission 64 3 Module Calendar: Important Dates & Overview Below “WS” stands for “Worksheet” and “TT” stands for “timetable” and “A” stands for “Appendix” (located at the back of our textbook). Week 1 1 1 1 2 2 2 2 3 3 3 3 4 4 4 4 5 5 5 5 ∗6 6 6 6 7 7 7 7 Lecture date Unit Homework Mon, Feb 10, 2025 1.1(a) WS1 Tues, Feb 11, 2025 1.1(b) WS1 Wed, Feb 12, 2025 1.2 (p. A9) no. 17, 19, 27, 35, 39, 57, 59, WS1 Fri, Feb 14, 2025 1.3 (p. A9) no. 43, 45, 47, 49, 51, 53, 55, 65, WS1 Mon, Feb 17, 2025 1.4 (p. A33) no. 23, 27, 29, 31, 45, 61, 65, 67, WS2 Tues, Feb 18, 2025 1.5 (p. 17) no. 1, 35 - 45 odd, WS2 Wed, Feb 19, 2025 1.6 (p. 42) no. 33, 35, 37, 45, 47, 49, 51, WS2 Fri, Feb 21, 2025 2.1 WS2 Mon, Feb 24, 2025 2.2 (p. 92) no. 5, 7, 9, 19, 21, 29, 31, 35, 37, WS3 Tues, Feb 25, 2025 2.3 (p. 102) no. 1, 11-33 odd, 37, 41, 49, WS3 Wed, Feb 26, 2025 2.4 (p. 113) no. 1, 19, 23, WS3 Fri, Feb 28, 2025 2.5(a) (p. 124) no. 3, 5, 9, 19, 21, 23, 33, 35, 43, 49, WS3 Mon, Mar 3, 2025 2.5(b) continue above problems, WS4 Tues, Mar 4, 2025 2.6 (p. 137) no. 1, 3, 7, 9, 15-31 odd, WS4 Wed, Mar 5, 2025 3.1 (p. 149) no. 5, 7, 19, 21, 23, 25, 33, WS4 Fri, Mar 7, 2025 3.2 (p. 161) no. 1, 3, 5, 7, 21-31 odd, 41, WS4 Mon, Mar 10, 2025 3.3(a) (p. 181) no. 3-33 odd, 37, 39, 49, (p. 189) 1-29 odd, 33, 35, WS5 Tues, Mar 11, 2025 3.3(b) continue above problems, WS5 Wed, Mar 12, 2025 3.4 (p. 197) no. 1-27 odd, 35, 39, WS5 Fri, Mar 14, 2025 3.5(a) (p. 206) no. 7-55 odd and not exponential, WS5 Mon, Mar 17, 2025 3.5(b), Fri TT continue above problems, WS6 Tues, Mar 18, 2025 3.6 (p. 52) no. 3, 15, 17, 21, (p. 206) 7-55 odd exponential, WS6 Wed, Mar 19, 2025 3.7 (p. 64) no. 5, 7, 13, 19, 69-71 odd, 75, 77 (p. 224) 63-75 odd, WS6 Fri, Mar 21, 2025 Public Holiday Mon, Mar 24, 2025 UP Test Week Tues, Mar 25, 2025 UP Test Week Wed, Mar 26, 2025 UP Test Week Fri, Mar 28, 2025 UP Test Week continues on next page... 4 Week 8 8 8 8 8 9 9 9 9 10 10 10 10 11 ∗ 11 11 11 12 12 ∗ 12 12 13 13 13 13 14 14 14 14 15 15 15 15 16 16 16 16 Lecture date Unit Homework Mon, Mar 31, 2025 3.8 (p. 214) no. 5-21 odd, 27-33 odd, WS7 Tues, Apr 1, 2025 3.9(a) (p. 224) 3-39 odd, 45-55 odd, WS7 Wed, Apr 2, 2025 3.9(b) continue above problems, WS7 ∗Lecture Videos∗ 3.10 (p. 266) 1, 3, 5, 11-15 odd, 19-23 odd, 35-43 odd, WS7 Fri, Apr 4, 2025 4.1(a) (p. 286) 1-13 odd, 29-47 odd, 51-65 odd, WS7 Mon, Apr 7, 2025 4.1(b) continue above problems, WS8 Tues, Apr 8, 2025 4.2(a) (p. 295) no. 9-17 odd, WS8 Wed, Apr 9, 2025 4.2(b) continue above problems, WS8 Fri, Apr 11, 2025 4.3(a) (p. 305) no. 1, 5, 9-29 odd 29, WS8 Mon, Apr 14, 2025 UP Recess Tues, Apr 15, 2025 UP Recess Wed, Apr 16, 2025 UP Recess Fri, Apr 18, 2025 Public Holiday Mon, Apr 21, 2025 Public Holiday Tues, Apr 22, 2025 4.3(b), Mon TT continue above problems, WS9 Wed, Apr 23, 2025 4.4 (p. 316) 9-69 odd, WS9 Fri, Apr 25, 2025 4.5 (p. 327) no. 1-19 odd, WS9 Mon, Apr 28, 2025 Public Holiday Tues, Apr 29, 2025 4.6(a) (p. 342) no. 3, 7, 9, 13, 15, 19, 21, 25, WS10 Wed, Apr 30, 2025 4.6(b), Mon TT continue above problems, WS10 Fri, May 2, 2025 4.7 (p. 361) 1-25 odd, 29-53 odd, WS10 Mon, May 5, 2025 UP Test Week Tues, May 6, 2025 UP Test Week Wed, May 7, 2025 UP Test Week Fri, May 9, 2025 UP Test Week Mon, May 12, 2025 5.1 (p. 381) no. 1(a), 5, WS11 Tues, May 13, 2025 5.2(a) (p. 394) no. 1, 5, 7, WS11 Wed, May 14, 2025 5.2(b) continue above problems, WS11 Fri, May 16, 2025 5.2(c) continue above problems, WS11 Mon, May 19, 2025 5.3(a) (p. 406) 25-53 odd, WS12 Tues, May 20, 2025 5.3(b) continue above problems, WS12 Wed, May 21, 2025 5.4 (p. 415) 1-23 odd, 27-53 odd, WS12 Fri, May 23, 2025 5.5(a) (p. 425) no. 1-53 odd, 59-79 odd, WS12 Mon, May 26, 2025 5.5(b) continue above problems, WS13 Tues, May 27, 2025 5.5(c) continue above problems, WS13 Wed, May 28, 2025 5.5(d) continue above problems, WS13 Fri, May 29, 2025 UP Recess tutorials week by week schedule on next page... 5 Tutorials Week by Week Week 1. (Feb 10 - 14) No tutorials. Week 2. (Feb 17 - 21) Tutorial Activity 1 - Attendance Required Week 3. (Feb 24 - 28) Tutorial Activity 2 - Attendance Required Week 4. (Mar 3 - 7) Tutorial Activity 3 - Attendance Required Week 5. (Mar 10 - 14) Tutorial Activity 4 - Attendance Required Week 6. (Mar 17 - 21) Practice Problems Set 1 - Attendance Not Required Week 7. (Mar 24 - 28) Semester Test Week. No tutorials. Week 8. (Mar 31 - Apr 4) Tutorial Activity 5 - Attendance Required Week 9. (Apr 7 - 11) Tutorial Activity 6 - Attendance Required Week 10. (Apr 14 - 18) UP Recess. No tutorials. Week 11. (Apr 21 - 25) Practice Problems Set 2 - Attendance Not Required Week 12. (Apr 28 - May 2) Practice Problems Set 3 - Attendance Not Required Week 13. (May 5 - 9) Semester Test Week. No tutorials. Week 14. (May 12 - 16) Tutorial Activity 7 - Attendance Required Week 15. (May 19 - 23) Tutorial Activity 8 - Attendance Required Week 16. (May 26 - 30) Practice Problems Set 4 - Attendance Not Required The General Rule: If we have a normal, full week (no holidays, etc.) then tutorial attendance is required, and you will work on a tutorial activity. If we don’t have a normal, full week, then tutorial attendance is not required, and you will work on a practice problem set. Attendance Required Tutorials: You must attend the tutorial group assigned to you in your timetable. Late registration students (after Feb 6th): You must register for a tutorial by emailing wtw114@up.ac.za (attach your late registration papers). You must attend your registered tutorial group. Attendance Not Required Tutorials: You do not have to attend your assigned/registered tutorial group. You can attend any tutorial group you want. 6 Course details A Welcome Welcome to WTW114 Calculus 2025! We are happy that you are joining us and want to encourage everyone to fully engage with the module— take it upon yourself to seize upon (and to create!) opportunities to interact with fellow students and staff so that we may grow a vibrant learning environment. The theme for this class is Work hard on maths every day, then success will come your way. We wish you all the best with WTW114 as well as all your other modules. The WTW114 Team Aim of the module Calculus provides us with a powerful tool to solve mathematical problems as well as real world problems that typically arise in Physics, Biology, Engineering and Economics. The emphasis in WTW114 is twofold. To equip students with the analytical skills required to solve such mathematical and real world problems, and to develop the methodological techniques necessary for mathematical proof. This module prepares students for courses in Advanced Calculus and Analysis that they will meet in their second and third years of study. B Organization B.1 Textbook James Stewart, Single variable calculus: Early transcendentals, International Metric Ed, 9th ed.1 1 You are encouraged to read the few pages on the “Principles of Problem Solving” (p. 71). 7 B.2 Staff (a) Dr Christopher Michael Schwanke (course coordinator) Vetman Building 1-8, christopher.schwanke@up.ac.za (b) Prof John van den Berg Mathematics Building 1-24.1, john.vandenberg@up.ac.za (c) Dr Ruaan Kellerman Mathematics Building 2-28 ruaan.kellerman@up.ac.za (d) Miss Baphumelele Nxala (module administrator) Mathematics Building 2-35, baphumelele.nxala@up.ac.za (e) All Admin Queries wtw114@up.ac.za B.3 Communication All admin related module correspondence should be sent to wtw114@up.ac.za. If you have a mathematical content question however, you may email any of the staff members listed above directly. Whilst every effort will be made to respond to your query quickly, please be aware that with a class of several hundred students, this will not always be possible. Announcements will be made via clickUP. B.4 Consulting hours Details on how to book a consultation with a staff member are available on clickUP. B.5 Lectures All lectures will be held face-to-face on campus. Any changes will be communicated via clickUP. You should have four scheduled time slots for lectures per week. Due to the substantially large size of this class, we offer three lectures per day on the days we do have lectures. As such, our lectures are organized in three groups. You choose which group you want to join and then just show up. No admin needed from you! We highly recommend that you, if possible, stick with one lecture group for the duration of the semester! The three lecture groups are taught by three different lecturers, whom each have different teaching styles, and go at slightly different paces. Caution! Each lecture group can hold at most 260 students, which is much smaller than the number of students in this class. If you attend a lecture group that is full, you must, if at all possible, switch to another group. The lecture schedule is below. (HB is the Humanities Building, and “vd” is short for “van der”.) Monday –Group G01 - 10:30 - 11:20 - Muller Hall –Group G02 - 7:30 - 8:20 - Centenary 1 –Group G03 - 11:30 - 12:20 - vd Bijl Hall Tuesday –Group G01 - 7:30 - 8:20 - Te Water Hall –Group G02 - 8:30 - 9:20 - Centenary 4 –Group G03 - 9:30 - 10:20 - Centenary 4 8 Friday –Group G01 - 8:30 - 9:20 - Muller Hall –Group G02 - 9:30 - 10:20 - vd Bijl Hall –Group G03 - 10:30 - 11:20 - HB 4-2 Wednesday –Group G01 - 8:30 - 9:20 - Muller Hall –Group G02 - 9:30 - 10:20 - vd Bijl Hall –Group G03 - 7:30 - 8:20 - vd Bijl Hall • Lecture Group G01 will be taught by Dr. Schwanke. • Lecture Group G02 will be taught by Dr. Kellerman. • Lecture Group G03 will be taught by Prof. van den Berg. Note that there will also be short “mini lectures” in video format posted on clickUP throughout the semester. The content of these videos is examinable! The reason we need to make these videos is because we lost two weeks of lectures this year due to the implementation of the two semester test weeks. B.6 Tutorials (also called Practicals) All tutorials will be held face-to-face on campus in two-hour sessions. Any changes will be communicated via clickUP. We have six timeslots for WTW 114 tutorials. You should have one scheduled time slot for tutorials/practicals per week. Officially, UP allocates three hours per tutorial session per week, but again, face-to-face tutorials will be held for only two hours per week. For the third hour, we will present solutions to the tutorial exercises on ClickUP. All first-year NAS students registered on or before Feb 6: Your tutorial timetable is set centrally by the faculty. You must attend the tutorial session allocated to you on your timetable! Switching tutorial sessions is not allowed for any reason. All other students: You must send an email to wtw114@up.ac.za to register for a tutorial group. Please note that we may not be able to accommodate your first choice, as some of the venues may be full. You must attach a copy of your timetable, and, if applicable, your late registration papers to your email. Group T01 –Tues - 14:30 - 16:30 - EMS 4-151 Group T02 –Wed - 10:30 - 12:30 - North Hall Group T03 –Thurs - 10:30 - 12:30 - EMS 4-150 and EMS 4-151 (go to either one of these venues, but if one of the venues is full, go to the other) Group T04 –Tues - 10:30 - 12:30 - South Hall and Theology 1-9 (go to either one of these venues, but if one of the venues is full, go to the other) Group T05 –Wed - 14:30 - 16:30 - HB 4-1 and HB 4-3 (go to either one of these venues, but if one of the venues is full, go to the other) Group T06 –Mon - 13:30 - 15:30 - Centenary 6 9 During eight of the tutorial sessions, you will be working on tutorial activities for a grade in teams of four. Students will form the teams themselves, so you may want to liaise with anyone you study with before you choose a tutorial team. See Section B.5 for more information on these tutorial activities. (Note that in WTW114 a “practical” is the same thing as a “tutorial.”) You should keep these time slots open for course activities. You should complete the exercises in this study guide of all the units that were covered in lectures during the week. B.7 Code of conduct We are not only facilitating learning in a module, we are also preparing you for the world of work. We expect you to adhere to the code of conduct as spelled out in the Escalation policy of UP. Communication via email When you email your lecturer, you have to use a respectful tone and include all the following aspects: • A clear and explanatory subject line; • Your full name and surname at the end of the mail; • Your student number; • The module involved; and • Short and clear message. Compliments and complaints You are more than welcome to express your appreciation to your lecturer or tutor and supply feedback about aspects of the course that you enjoy and find valuable. If you have a query or complaint, you have to submit it in writing with specifics of the issue or the nature of the complaint. It is imperative that you follow the procedure outlined below in order to resolve your issues: 1. Consult the lecturer concerned about your complaint/concerns. If the matter has not been resolved, 2. consult the class representative (the primary function of the Class Representative is to serve as a two-way communication channel between the class and the lecturer). If the matter has not been resolved, 3. consult the module coordinator (large modules with multiple lecturers). If the matter has not been resolved, 4. consult the Head of Department. If the matter has still not been resolved, 5. consult with the Dean of the Faculty. C Assessment and related matters All class tests, semester tests and the exam will be conducted on campus. The following serves as a guideline. 10 C.1 Material for tests and the Examination Material for tests and the Examination will be posted on clickUP. Dates for the two Semester Tests are given on the UP Website. Please note, however, that these dates are provisional and might change. In the event that they do change, you will be given advance warning. Tests and exams in this course aim primarily to test your understanding of the relevant mathematical concepts, as opposed to the rote application of recipes and memorization of proofs. This may be done using a variety of questions which test your ability to perform certain calculations, your understanding of definitions, theorems and their proofs, your ability to solve mathematical problems, and, your ability to give mathematical formulations of real-world problems (so called word sums). Also take note of the following: 1. Student cards must be presented on request during tests and examinations. 2. The removal of examination papers from the examination venue is a transgression of the examination rules and is regarded as a serious offence. 3. All test queries must be made within 3 days after tests are handed back to students. C.2 Absence from assessments If you are absent from a Tutorial Activity or Semester Test 2, you must submit to a sick note via clickUP within 3 working days of the test being written. You must present convincing proof of the reason for your absence, for example a medical certificate (see below). In the case of a normal invigilated exam, the relevant faculty office should be informed of the absence. There will be no “make ups” for tutorial activities. If you miss a tutorial activity for a valid reason (with proof), then that those marks will be excluded when your total mark is calculated. If you missed a tutorial activity due to illness, you must submit a doctor’s note on clickUP. If you missed a tutorial activity due to late registration, you must submit your late registration papers on clickUP. Missed worksheet submissions are not excluded for any reason, but we offer bonus marks for those instead. Thus you can miss a few worksheets and still get full marks for them overall. If you miss Semester Test 2 (and you have acceptable excuse), then you may write a Sick Test at a time that will be announced. It will cover the work of both semester tests. If you miss Semester Test 1 for whatever reason, your Semester Test 2 score will simply count as your Semester Test 1 score as well. • Valid original sick notes are accepted if issued by a medical doctor registered at the Health Professions Council of South Africa (HPCSA). The only other type of sick note that is accepted are those issued by an Advanced Practice Nurse (a registered nurse with a postgraduate qualification) as determined by the South African Nursing Council who has a BHCF practice number, provided that the diagnosis falls only within their specific field of specialisation. • An affidavit will only be accepted if supported by substantiating documentation, e.g. case report or criminal charge with case number obtained from a police station, valid medical certificate for injuries, a death certificate for a funeral, etc. Please note that submission of fraudulent sick notes and affidavits is a criminal offense, which will lead to disciplinary action and may result in dismissal. 11 C.3 Practice Problems Practice problems are given for each and every unit in this study guide. It is extremely important that you attempt to complete as many as these practice problems as you have time for before starting the weekly worksheet! However, these practice problems are not to be submitted for a grade. Thus these are a great, low-stress way to practice calculus! C.4 Weekly Worksheets Most weeks you will be given a weekly worksheet consisting a set of problems to complete before your next week’s tutorial session. These problems will be more difficult than the practice problems you were given. That’s one reason it’s critical to start with the practice problems! Although the worksheets are not marked, you will submit them and receive a small amount of marks for completing the worksheet. In order to receive marks for worksheet submissions, you must attempt all of the problems and show sufficient effort for each one! Marks for worksheet submissions are given on an “all or nothing” basis. Worksheets are submitted online. Details on how to submit can be found on ClickUP. Unless otherwise specified on ClickUP, all worksheets will be due on Mondays at 7:00am. No late submissions of worksheets are accepted for any reason, so be sure to not wait until the last minute! However, you can miss three worksheets and still receive full marks in total for the worksheets. Although these worksheets are not marked, they play a fundamental role in the tutorial activities, which are marked, see next section. C.5 Tutorial Activities Provisionally, eight weeks of tutorials are reserved for “tutorial activities”. Students will work on these tutorial activities in teams of four, with no more than two teams of less than four. There will be no teams more than four in size. These tutorial activities consist of three questions to be worked on, and turned in, by each team. C.6 Practice Problem Sets Provisionally, four weeks of tutorials are reserved for “practice problem sets”. These are similar to tutorial activities, except they are not mandatory and not submitted for a mark. Nonetheless, they prepare you for the semester tests and exam, as so they are just as important as tutorial activities! C.7 Semester Tests There will be two semester tests given in this module. Times and venues are available on the university’s website, but those could potentially change. The course coordinator will clearly communicate with you on ClickUP regarding the times, venues, and content of the semester tests. C.8 How Will Everything Be Marked? With the exception of both semester tests, every single question written for a grade will be graded out of five marks. That includes all tutorial activities. The rules for the marking tutorial activities are as follows: –5. Perfect answer! –4. Only very minor error(s) present, solid understanding of the material clearly demonstrated. 12 –3. There exist more than just very minor errors, a passworthy level of understanding has been demonstrated. –2. There exist more than just very minor errors, an unpassworthy level of understanding has been demonstrated, but the work is close to passworthy. –1. The work is not close to passworthy, but at least some meaningful progress toward a correct answer has been shown (e.g. at least writing down a relevant definition). –0. Not close to passworthy, no meaningful progress toward a correct answer shown. –No half marks will be given. For Semester Tests 1 and 2, the marking is almost the same, except each question will be worth 15 marks: –15. Perfect answer! –12. Only very minor error(s) present, solid understanding of the material clearly demonstrated. –9. There exist more than just very minor errors, a passworthy level of understanding has been demonstrated. –6. There exist more than just very minor errors, an unpassworthy level of understanding has been demonstrated, but the work is close to passworthy. –3. The work is not close to passworthy, but at least some meaningful progress toward a correct answer has been shown (e.g. at least writing down a relevant definition). –0. Not close to passworthy, no meaningful progress toward a correct answer shown. –No in-between marks will be given. C.9 Semester Mark There are 380 total marks available prior to the semester exam. The breakdown of these marks is as follows: 2 marks each × 10 worksheets = 20 marks Worksheet Submissions: Tutorial Activities: 15 marks each × 8 tutorial activities = 120 marks Semester Test 1: 120 marks Semester Test 2: 120 marks Total: 380 marks Your semester mark will be given as a percentage out of 100, rounded to the nearest integer. So for example: 285/380 marks = 75% 190/380 marks = 50% 152/380 marks = 40% =⇒ exam admission Note: There will 13 worksheets to be submitted for a mark. Thus there will be the opportunity to earn six bonus marks by submitting all 13 worksheets! 13 C.10 Cumulative Semester Test 2 Semester Test 2 will be cumulative, meaning it will cover everything from the first week of class up to where we are in the class at the time Semester Test 2 is written. Your Semester Test 2 score will replace your Semester Test 1 score provided you score better on Semester Test 2 than Semester Test 1. For example, if you score 54 on Semester Test 1 and 114 on Semester Test 2, then your official grade book will show a score of 114 for Semester Test 1 and a score of 114 for Semester Test 2. Your Semester Test 1 score got replaced by your improved Semester Test 2 score! However, for example, if you score 90 on Semester Test 1 and 50 on Semester Test 2, then your official grade book will show a score of 90 for Semester Test 1 and 50 for Semester Test 2. Your Semester Test 1 score did not get replaced since your Semester Test 2 score was lower. Again, Semester Test 2 will only replace your Semester Test 1 score if you do better on Semester Test 2. Semester Test 1 cannot affect your Semester Test 2 score in any way. Two key takeaways from this policy are the following. (i) Your learning in WTW 114 should be permanent. (ii) You can always keep improving in WTW 114, and you get rewarded for doing so. C.11 Missing Tutorial Activities and Semester Tests Each Tutorial Activity that is missed with a valid excuse (e.g. sick with a doctor’s note) cannot be made up but can be excluded from the calculation of your marks. If you miss Semester Test 1 for any reason, you will score a zero but your Semester Test 2 score will later replace it. If you miss Semester Test 2 with valid excuse with proof (e.g. sick with doctor’s note), your mark for the Special Test/Sick Test will be used in its place in the above calculation for the Semester Mark. However, the Special Test/Sick Test will not replace your Semester Test 1 score, even if you score better on the Special Test. If you miss Semester Test 1 and write Semester Test 2, then you do not need to take the Special Test/Sick Test. In fact, you do not qualify to write the Special Test/Sick Test in this case. C.12 Examination admission A minimum Semester Mark of 40% is required to be admitted into the examination. C.13 Semester Examination Only those who are admitted into the examination will receive a semester exam mark. The semester exam will be graded out of 120 marks, just like the two semester tests. Your Semester Exam mark will be given as a percentage out of 100, rounded to the nearest integer. C.14 Final Mark Your Final Mark will be computed as follows: 14 • Semester Mark: 60% • Examination Mark: 40% As such, your final mark is calculated using the following formula: Final Mark = 0.6 × (Semester Mark) + 0.4 × (Examination Mark) To pass the module, a Final Mark of at least 50% is required together with a sub-minimum of 40% for the Examination. C.15 Supplementary Examination A student who has a final mark between 40% and 49%; will not have passed the module, but will have qualified for a Supplementary Examination. A student who is admitted to the Supplementary Examination must obtain a minimum mark of 50% for this exam in order to pass the course, regardless of their Semester Mark. D Contact time and study hours This module carries a weight of 16 credits, indicating that, on average, a student should spend some 160 hours to master the required skills (including time for preparation for tests and the examination). This means that, on average, you should devote some 11.5 hours of study time per week to this module. E Disciplinary issues The policy of the Department is to refer all incidents in which there is a suspicion of dishonesty or other irregularity to the Disciplinary Committee of the University. Plagiarism is a serious form of academic misconduct. It involves both appropriating someone else’s work and passing it off as one’s own work afterwards. Thus, you commit plagiarism when you present someone else’s written or creative work (words, images, ideas, opinions, discoveries, artwork, music, recordings, computer-generated work, etc.) as your own. Only hand in your own original work. Indicate precisely and accurately when you have used information provided by someone else. Referencing must be done in accordance with a recognised system. Indicate whether you have downloaded information from the Internet. For more details, visit the library’s website: http://www.library.up.ac.za/plagiarism/index.htm. 15 Theme 1: Functions Unit 1.1: Logic/Proofs 2 lecture Note: This unit was added in order to help students with their proofwriting. Although proofwriting has always been expected of students in this course, there was little time given in class to help students prepare for this responsibility. We have added this unit to address this issue. Textbook: None Learning outcomes: On completion of this unit you should be able to 1. understand basic symbolic logic 2. be able to fill in truth tables 3. be able to use mathematical qualifiers 4. be able to write direct mathematical proofs 5. be able to write mathematical proofs by contradiction 6. be able to write mathematical proofs by contraposition 7. be able to write mathematical proofs via mathematical induction 8. to be able to disprove false mathematical statements using a counterexample Problems: None from the textbook, but there will be some problems in the weekly worksheets to help you practice these important concepts. Unit 1.2: Numbers, intervals and inequalities 1 lecture Textbook: Appendix A, pp. A2–A6. Learning outcomes: On completion of this unit you should 1. know what the symbols N, Z, Q, R and ∅ (see additional notes) stand for. 2. be able to use set-builder notation to describe sets. 3. be able to use the union and the intersection of two sets, as well as the compliment of one set with another (see additional notes), to describe a set. 4. be able to use interval notation and set-builder notation to describe intervals. 5. know the rules for inequalities and be able to use them to solve inequalities. 16 6. be able to use standard bracket notation for finite sets. Additional notes: 1. Let S be a set. We use the notation x ∈ S to denote that x is an element of S . A set S is contained in a set T , denoted by S ⊂ T , if x ∈ S implies that x ∈ T . 2. On page A3, study the paragraph explaining the following ideas: set; element of a set; the union S ∪ T of sets S and T ; the intersection S ∩ T of sets S and T ; set-builder notation. 3. The empty set, written as ∅, is the set that contains no elements. 4. Let S and T be sets. Then S compliment T , written as S \ T , is the set which consists of all elements in S that is not in T . 5. You must remember the following special symbols that will be used in all the mathematics modules: R is the set of all the real numbers. Q is the set of all the rational numbers. Z is the set of all the integers. N is the set of all the natural numbers. 6. In set-builder n notation, o Q = mn | m, n ∈ Z and n , 0 Z = {. . . , −3, −2, −1, 0, 1, 2, 3, . . .} N = {1, 2, 3, . . .} 7. In list 1 on page A4, study the set-builder notation in which the different types of intervals are expressed. Here are some examples: (a) Describe the set {x ∈ Z | −4 ≤ x < 1} in your own words and give all its elements. Solution. It is the set of all integers that are greater or equal to −4 and less than 1. Therefore {x ∈ Z | −4 ≤ x < 1} = {−4, −3, −2, −1, 0}. (b) Write the following sets as intervals or as the union or intersection of intervals: i. {x ∈ R | 1 ≤ x < 3} = [1, 3) ii. {x ∈ R | 0 ≤ x ≤ 3 and 1 < x < 4} = [0, 3] ∩ (1, 4) = (1, 3] iii. {x ∈ R | 0 ≤ x ≤ 3 or 1 < x < 4} = [0, 3] ∪ (1, 4) = [0, 4) iv. {x ∈ R | −3 ≤ x < −1 or 0 ≤ x ≤ 2} = [−3, −1) ∪ [0, 2]. 8. Simplify the following expressions: i. (−∞, 3] \ (0, 4) = (−∞, 0] ii. [3, 4] \ ∅ = [3, 4] iii. ([3, 4] ∪ (4, 5)) ∩ ∅ = ∅ 9. The Rules for Inequalities (list 2 on page A4) is a useful summary of the rules for solving inequalities. Study Examples 1, 2, 3, and 4. 10. In Example 3 (page A5) the inequality x2 − 5x + 6 ≤ 0 is solved. Get used to making use of what is called the “visual method” and draw the parabola y = x2 − 5x + 6, showing its intersection with the x-axis. 17 Then the solution is all x for which y ≤ 0, that is, 2 ≤ x ≤ 3. The solution set is the interval [2, 3]. 11. In Example 4 the inequality x3 + 3x2 − 4x > 0 is solved. First factorise y = x3 + 3x2 − 4x = x(x2 + 3x − 4) = x(x + 4)(x − 1). Then draw the 3rd degree polynomial by observing for example that if x = −1 then y = 6. Solution: −4 < x < 0 or x > 1, that is the set (−4, 0) ∪ (1, ∞). 18 Unit 1.3: The absolute value 2 lectures Textbook: Appendix A, pp. A6–A9. Learning outcomes: On completion of this unit you should be able to 1. write down and use the definition of the absolute value of a number. 2. solve absolute value inequalities. Additional notes: 1. One of the most important applications of the absolute value will be the type discussed in Example 5 on page A7. Study it well and rewrite the following expressions without the absolute value symbol: (a) |x + 1| (b) |x2 − 1| (c) |x2 + 1| (d) |2x − 1| 2. On page A7 in list 6, there are three rules that are helpful for solving absolute value equations and inequalities. (One can also solve these equations by making use of the definition of the absolute value.) In Example 7 we must solve |x − 5| < 2. That means the number x − 5 is distance less than 2 units away from 0, that is, −2 < x − 5 < 2. So 3 < x < 7 and the solution set is the open interval (3, 7). 3. The properties in block 5 (p. A7) can be proved by using property 4, |a| = √ 4. Property 4, |a| = a2 , also implies that |a|2 = a2 . 19 √ a2 . Unit 1.4: Trigonometry 1 lecture Textbook: Appendix D, pp. A24–A33. Learning outcomes: On completion of this unit you should be able to 1. find the sin, cos, tan, cosec, sec and cot of angles in radians. 2. solve simple trig equations. 3. write down and use the trigonometric identities. Additional notes: 1. An angle has a vertex and two sides (Figure 1, p. A24) and can be measured in degrees or radians. Formula 1 on page A24 gives the conversion rule: π rad = 1800 . In Calculus, we use radians to measure angles. 2. Figure 1 on page A24 shows a sector OAB of a circle with an angle θ with vertex the center of the circle and θ subtending the arc AB “of length a”. The circle has radius r. We know the definition of the length of a straight line. Without properly defining what the length of an arc is, we will work from the starting point that the circumference of a circle is 2π times the radius of the circle. We cannot prove this here, since then we would need the definition of the length of an arc. By using the circumference of a circle, we can prove (see p. A24) that θ = ar . We can use this formula to determine the length of an arc of a circle. With this formula one can now see that in a circle with radius 1, the circumference of 2π is subtended by an angle of 2π radians. 3. Study the definitions of the standard position of an angle and what is meant by a positive angle and a negative angle on page A25. 4. Study and memorize the formulas in lists 4 and 5 on page A26 very well—especially the new ones, namely • the reciprocal of sin θ, namely csc θ; • the reciprocal of cos θ, namely sec θ; • the reciprocal of tan θ, namely cot θ. 5. Study and memorize the special triangles at the bottom of page A26 and/or the unit circle. 6. Study Example 3 (p. A27) and use the technique in the example to do Exercise D (p. A32) no. 23. Exercises: Find sin 0, sin π4 , sin π6 , sin π, sin 1, sin 2 and sin 3 by using a calculator. 7. Example: Find all values of x in the interval [0, 2π] that satisfy the equation 2 cos x − 1 = 0. Solution: From 2 cos x − 1 = 0 follows that cos x = 12 . Using one of the special triangles gives one solution x = π3 . Since y = cos x is also positive in the fourth quadrant, x = 2π − π3 = 5π 3 is another solution. Exercises: Solve the following equations in [0, 2π] without a calculator: (a) 2 sin x − 1 = 0 20 (b) 2 sin2 x = 1 (c) tan x = 1 8. Example: Solve 3 sin x + 1 = 0 in [0, 2π]. (Use a calculator.) Solution: It follows that sin x = − 13 . Because x is in radians, switch the calculator from degrees to radians. Enter − 13 and find the inverse function of sin of − 31 , namely −0.34. There are solutions in the 3rd and the 4th quadrants, namely x = π + 0, 34 or x = 2π − 0.34 = 3.48 = 5.94. Exercise: Find all the solutions of the equation tan2 x − 9 = 0 in [0, 2π]. (Use a calculator.) Trigonometric Identities (p. A28) 9. Memorize list 7 and the basic Identity 8 sin2 θ + cos2 θ = 1. 10. Identity 9, tan2 θ + 1 = sec2 θ, follows from Identity 7 by dividing both sides by cos2 θ : 1 1 (sin2 θ + cos2 θ) = , 2 cos θ cos2 θ sin θ cos θ 2 that is, cos 2 θ + cos2 θ = sec θ, and so 2 2 sin θ 2 + 1 = sec2 θ. Thus tan2 θ + 1 = sec2 θ. cos θ 11. Identity 10, 1 + cot2 θ = cosec2 θ, follows by dividing both sides of Identity 7 by sin2 θ. Do it as an exercise. 21 12. The following identities are well-known from school and must be memorized: (10a) sin(−θ) = − sin θ (10b) cos(−θ) = cos θ (12a) sin(x + y) = sin x cos y + cos x sin y (12b) cos(x + y) = cos x cos y − sin x sin y 13. The identities (13a), (13b), (16a), (16b), (17a), (17b), (18a) and (18b) on page A29 and A30 can be proved using the previous ones. Now prove: (16a) sin 2x = sin(x + x) = . . . (16b) cos 2x = cos(x + x) = . . . Also prove (17a), (17b), (18a) and (18b). Graphs of the Trigonometric Functions 14. In Grade 11 you used to draw the function f (x) = sin x or y = sin x in the xy-system where the y-axis represented the real numbers and the x-axis represented degrees. The same for y = cos x and y = tan x. On pages A30 and A31 you see the graphs of y = sin x, y = cos x and y = tan x where the x-axis represents real numbers. In Calculus, if x is a real number, then sin x is found by interpreting x as x radians. Similarly for the other trigonometric ratios. 15. Example: Find all the values of x in the interval [0, 2π] satisfying 2 cos x + 1 < 0. Solution: We have to solve cos x < − 12 . We first solve cos x = − 12 . π 4π x = π − π3 = 2π 3 or x = π + 3 = 3 . Sketch y = cos x. 4π 2π 4π From the graph, 2π 3 < x < 3 . So the set of solutions is ( 3 , 3 ). 22 Unit 1.5: Functions and their graphs 2 lectures Textbook: Section 1.1, p. 8. Learning outcomes: On completion of this unit you should be able to 1. determine whether a rule defines a function. 2. find the intended domain of a function (in case a domain is not specified). 3. write absolute value functions as piecewise defined functions. 4. determine whether a function is even, odd or neither. Additional notes: 1. Study the definition of a function, its domain, range, independent variable and dependent variable (pages 8 & 9). We denote the domain and range of a function f by D f and R f , respectively. 2. The set E in the definition of a function f on p. 8 is called the codomain of f . 3. We use the notation f : D → E to denote a function f with domain D and codomain E. 4. We denote the set {(x, y) | x ∈ D, y ∈ E} by D × E. 5. On p. 9 we see that the graph of a function f with domain D is the set of ordered pairs {(x, f (x)) | x ∈ D} = {(x, y) | y = f (x), x ∈ D}. Note that for a function f : D → E the graph {(x, f (x)) | x ∈ D} ⊂ D × E. completely determines f . For example, the function f with f (x) = 2x + 3, x ≥ 0, can be thought of as the set {(x, y) | y = 2x + 3, x ≥ 0}. Therefore we also refer to f as the function y = 2x + 3, x ≥ 0. Example: Does x2 + y2 = 1 define a function with domain [−1, 1]? Solution: The graph {(x, y) | x2 + y2 = 1} is the circle with center the origin and radius 1 and for example, x = 0 is associated with y = 1 and y = −1. Therefore x2 + y2 = 1 does not define a function. (Read about the “vertical line test” on p. 15). Exercise: Does y2 = x define a function with domain [0, ∞)? Give reasons for your answer. 6. Study Examples 1, 2 and 3 (pp. 9–10) and do the following exercise: Exercise: Sketch the graph of f (x) = x2 − 2x − 3, 0 < x < 4. What is the domain and what is the range of f ? 7. If the domain of a function f is not specified (and in most cases it is not specified), then it is understood that the domain of f is the largest possible set of real numbers x for which f (x) exists. 23 Injective, Surjective and Bijective Functions (p. 16) 8. Definition: Let D and E be sets of real numbers. A function f : D → E is (i) one-to-one (injective) if for all x1 , x2 ∈ D, if x1 , x2 then f (x1 ) , f (x2 ); (ii) onto (surjective) if for every y ∈ E there exists x ∈ D so that f (x) = y; (iii) bijective if it is both one-to-one and onto. 9. Remark: Note the following. (i) Let D and E be sets of real numbers and f : D → E a function. f is onto if and only if E is the range of f . (ii) Every function is a surjection onto its range. (iii) A function f : D → E is injective if and only if for all x1 , x2 ∈ D, if f (x1 ) = f (x2 ) then x1 = x2 . (iv) If a function f is strictly increasing or strictly decreasing then it is one-to-one. 10. Example: The function f : (0, ∞) → (1, ∞) given by f (x) = 1x + 1 is bijective. First we show that f is injective. Let a, b ∈ (0, ∞). Assume that f (a) = f (b). Then 1 1 + 1 = + 1. a b Therefore a1 = 1b so that a = b. 1 . Because y > 1, y − 1 > 0. Now we show that f is surjective. Let y ∈ (1, ∞). Let x = y−1 1 Therefore x = y−1 is well defined and x > 0; that is, x ∈ (0, ∞). We compute f (x): f (x) = 1 1 y−1 + 1 = (y − 1) + 1 = y. Therefore f is surjective. Because f is both injective and surjective, it is bijective. 24 Piecewise Defined Functions (p. 16) 11. A piecewise defined function has a domain that is divided into pieces and has a different formula on each of the pieces. 12. Example: We write f (x) = |2x + 1| without the absolute value symbol: ( 2x + 1 if 2x + 1 ≥ 0 |2x + 1| = −(2x + 1) if 2x + 1 < 0 ( 2x + 1 if x ≥ − 21 Therefore f (x) = −2x − 1 if x < − 21 . The domain of f is R. 13. Example: Write f (x) = |x2 − 1| without the absolute value symbol and write down the domain of f. ( 2 ( 2 x −1 if x2 − 1 ≥ 0 x −1 if x ≤ −1 or x ≥ 1 2 |x − 1| = = 2 2 2 −x + 1 if x − 1 < 0 −x + 1 if − 1 < x < 1 The domain of f is R. Unit 1.6: New functions from old functions 2 lectures Textbook: Section 1.3, p. 36. Learning outcomes: On completion of this unit you should 1. be able to combine two functions f and g to form the new functions f + g, f − g, f g and gf and be able to determine the domains of these functions. 2. be able to form the composite functions f ◦ g and g ◦ f for given functions f and g and be able to determine the domains of the new functions. 3. be able to decide what the rules of the functions f and g are if a rule for the composite function f ◦ g is given. Additional notes: 1. Given any two functions f and g the following combinations are defined: • The sum f + g with ( f + g)(x) = f (x) + g(x). • The difference f − g with ( f − g)(x) = f (x) − g(x). • The product f g with ( f g)(x) = f (x)g(x). ! f f f (x) • The quotient with (x) = , g(x) , 0. g g g(x) • The composition f ◦ g with ( f ◦ g)(x) = f (g(x)). Make sure that you understand what the domains of these functions are. 2. Study Examples 6, 7 and 8 on pages 41 and 42. 25 Theme 2: Limits and Continuity Unit 2.1: The tangent and velocity problems 1 lecture Textbook: Section 2.1, pp. 78–81. Learning outcomes: On completion of this unit you should be able to 1. estimate the slope of a tangent line to a curve by calculating the limit of the slope of secant lines. Problems: none Unit 2.2: The limit of a function 1 lecture Textbook: Section 2.2, p. 83. Learning outcomes: On completion of this unit you should be able to 1. explain the informal idea of the limit of a function at a point and be able to interpret this idea graphically. 2. find the limit of a function at a point if the graph of the function is given. 3. explain what is meant by one-sided limits and be able to interpret these ideas graphically. 4. find lim f (x) by using the one-sided limits lim+ f (x) and lim− f (x) (only when necessary). x→a x→a x→a 5. explain the informal definition of the infinite limit lim f (x) = ∞ (and lim f (x) = −∞) and be able x→a x→a to interpret this idea graphically. Additional notes: 1. In Definition 1 on p. 83 there is, as in Grade 12, an informal and intuitive definition of the meaning of lim f (x) = L. x→a In Section 2.4 (p. 105) you will see the mathematically precise meaning that will make it possible to prove certain facts about limits. 26 One-sided Limits 2. The paragraph preceding Definition 2 (p. 86) is important because it shows why for the Heaviside function ( 0 if t < 0 H(t) = , 1 if t ≥ 0 lim H(t) does not exist and it introduces the idea of one-sided limits lim+ H(t) = 1 and lim− H(t) = t→0 t→0 t→0 0. Infinite Limits 3. Study Definitions 4 and 5 (pp. 89–90) for the meaning of lim f (x) = ∞ and lim f (x) = −∞. x→a x→a 4. Figures 9, 10, 11 and 12 (pp. 89–90) are very helpful. 5. Study Definition 6 (p. 90) for the meaning of a vertical asymptote of a curve y = f (x). 6. Study Examples 7 and 8 (p. 91). Unit 2.3: Limit laws 1 lecture Textbook: Section 2.3, p. 94. Learning outcomes: On completion of this unit you should be able to 1. use the appropriate limit law to find the limit of the sum, difference, product and quotient of two functions and the constant multiple of a function. 2. use the direct substitution property to find the limits of polynomials and rational functions. 3. determine whether a limit exists by evaluating one-sided limits. 4. write down and use the Squeeze Theorem. Remark: The limit laws can be proved by making use of the formal definition of a limit. However, we will not prove these laws in this module. Unit 2.4: Precise definition of a limit 1 lecture Textbook: Section 2.4, p. 105. Learning outcomes: On completion of this unit you should 1. understand the definition of a limit. 2. be able to use the definition of a limit to confirm simple limits. 27 Unit 2.5: Continuity 3 lectures Textbook: Section 2.5, p. 115. Learning outcomes: On completion of this unit you should be able to 1. determine whether a given function is continuous at a number a. 2. prove and use the theorems on the continuity of the combination of continuous functions (sum, difference, constant multiple, product, quotient and composite). 3. explain and use the Intermediate Value Theorem. Remarks: 1. Ignore any reference to exponents and logarithms in this section. Additional note: We give the proof of Theorem 4(3): If f is continuous at a and c is a constant then c f is continuous at a. Proof. Suppose f is continuous at a and c is a constant. Then lim (c f )(x) = lim c · f (x) x→a (definition of c f ) x→a = c · lim f (x) (by Law 3 on p. 95) = c · f (a) ( f is continuous at a) = (c f )(a) (definition of cf). x→a This proves that the function c f is continuous at a. Unit 2.6: Limits at infinity and horizontal asymptotes Textbook: Section 2.6, pp. 127–134 (skip pp. 135–137). Learning outcomes: On completion of this unit you should be able to 1. explain what is meant by the following limits: lim f (x) = L, lim f (x) = L, lim f (x) = ∞ x→−∞ x→∞ lim f (x) = ∞, lim f (x) = −∞, lim f (x) = −∞. x→∞ x→−∞ x→∞ x→−∞ 2. interpret limits at infinity graphically. 3. find horizontal asymptotes of a function. 28 1 lecture Theme 3: Differentiation Unit 3.1: Derivatives and rates of change 1 lecture Textbook: Section 2.7, p. 140. Learning outcomes: On completion of this unit you should be able to 1. write down and use the definition of the derivative of a function at a point. 2. find derivatives of functions by using the definition. 3. find the equation of a tangent line to a graph. Remark: Omit Examples 7 and 8. Additional notes: We will focus on the slope of a tangent line to curves and not on velocities and rates of change. Here is a summary of this section: 1. The derivative of a function f at a number a is the limit f (a + h) − f (a) h→0 h f (x) − f (a) = lim x→a x−a f ′ (a) = lim (Definition 4, p. 144) ((5), p. 144) if the limit exists. 2. If f ′ (a) exists, then m = f ′ (a) is the slope of the tangent line to the curve y = f (x) at the point P(a, f (a)) and the equation of the tangent line is y − f (a) = m(x − a). 3. To find the derivative of a polynomial of degree ≥ 3, one needs the following useful formula that holds for all real numbers a and b and all positive integers n: an − bn = (a − b)(an−1 + ban−2 + b2 an−3 + . . . + bn−1 ). Try to prove this by using the formula for the sum of a geometric progression, a + ar + ar2 + . . . + arn−1 = 29 a(rn − 1) . r−1 Unit 3.2: The derivative as a function 1 lecture Textbook: Section 2.8, p. 153. Learning outcomes: On completion of this unit you should 1. be able to write down and use the definition of the derivative function. 2. be able to sketch the graph of the derivative function if the graph of the function is given. 3. be able to write down what it means for a function to be differentiable at a point. 4. be able to write down what it means for a function to be differentiable on an interval. 5. know and be able to prove that a function that is differentiable at a point is continuous at that point and that the converse of the theorem is not true. 6. know the different notations for the derivative. 7. know the notation for higher derivatives and be able to find higher derivatives. Additional notes: 1. If f is a function, then the function f ′ that assigns to x the number f ′ (x) = lim h→0 f (x + h) − f (x) , if it exists, h is called the derivative of f (Definition 2, p. 153). 2. In Example 1 (p. 153), study the graphs of f and f ′ in Figure 2 (p. 154). Note that if f ′ (x) > 0 for each x on an interval, then f is increasing on that interval and that if f ′ (x) < 0 on an interval, then f is decreasing on that interval. (This is a theorem that will be proved in Theme 4). 3. Note that the derivatives of polynomials, root functions, exponential functions (see Unit 3.6), logarithmic functions (see Unit 3.9) and rational functions are continuous on their domains. 30 Unit 3.3: Differentiation rules 2 lectures Textbook: Section 3.1 (pp. 174–179) and Section 3.2 (pp. 185–189). Learning outcomes: On completion of this unit you should be able to 1. write down and use the rule for the derivative of a constant function. 2. write down and use the rule for the derivative of xn (n a natural number). 3. write down and use the rule for the derivative of a constant multiple of a function. 4. write down and use the rule to find the derivative of the sum, difference, product and quotient of differentiable functions. Remark: Omit the exponential functions (pp. 177–179) for now. Additional notes: 1. In Section 3.2 the rules for the derivative of the product and quotient of differentiable functions are proved. However, you do not need to memorize the proofs below. Just the rules themselves need to be memorized. 2. The Product Rule: Suppose f and g are differentiable functions. Let P(x) = f (x) · g(x). Then P(x) is differentiable and ! ! d d d [P(x)] = f (x) g(x) + f (x) g(x) dx dx dx or equivalently P′ (x) = f ′ (x)g(x) + f (x)g′ (x). Proof. First, we look at the quotient below. P(x + h) − P(x) f (x + h) · g(x + h) − f (x) · g(x) = h h f (x + h) · g(x + h) − f (x) · g(x + h) + f (x) · g(x + h) − f (x) · g(x) = h g(x + h) − g(x) f (x + h) − f (x) · g(x + h) + f (x) = h h Next, we explain why the following four limits exist. f (x + h) − f (x) = f ′ (x) h g(x + h) − g(x) lim = g′ (x) h→0 h lim f (x) = f (x) lim h→0 h→0 lim g(x + h) = g(x) h→0 (given f is differentiable) (given g is differentiable) (constant limit law) (g is differentiable implies g is continuous) From the above facts and the product limit law, we obtain lim h→0 f (x + h) − f (x) · g(x + h) = f ′ (x) · g(x) h g(x + h) − g(x) lim f (x) · = f (x) · g′ (x) h→0 h 31 (1) Finally, from the sum limit law, we obtain lim h→0 g(x + h) − g(x) f (x + h) − f (x) · g(x + h) + f (x) · = f ′ (x) · g(x) + f (x) · g′ (x) h h From equation (1) and above we see that lim P(x+h)−P(x) exists. Therefore P is differentiable and h h→0 d d d [P(x)] = f (x) · g(x) + f (x) g(x) as desired. dx dx dx 3. Before we prove the quotient rule, we first prove the reciprocal rule. The Reciprocal Rule: If g is differentiable and g(x) , 0, then − d g(x) d 1 = dx 2 dx g(x) g(x) or equivalently !′ 1 −g′ (x) . (x) = g g(x)2 Proof. We have d 1 = lim dx g(x) h→0 1 1 g(x+h) − g(x) h g(x) − g(x + h) = lim h→0 hg(x)g(x + h) −1 1 g(x + h) − g(x) = lim · lim g(x) h→0 g(x + h) h→0 h −1 1 d = · · g(x) g(x) g(x) dx (since g is differentiable in x, g is also continuous in x which means lim g(x + h) = g(x).) h→0 − d g(x) = dx 2 . g(x) Examples: ! d 1 −1 • = 2 dx x x ! d −2x 1 • = 2 . 2 dx x + 1 (x + 1)2 32 4. The Quotient Rule If f and g are differentiable and g(x) , 0 then d d d f (x) g(x) dx f (x) − f (x) dx g(x) , = dx g(x) [g(x)]2 that is !′ f g(x) f ′ (x) − f (x)g′ (x) . (x) = g [g(x)]2 Proof. We have ! d f (x) d 1 = f (x) · dx g(x) dx g(x) ! d 1 d 1 f (x) · + f (x) · = dx g(x) dx g(x) d − dx g(x) d 1 = f (x) · + f (x) · dx g(x) g(x)2 (product rule) (reciprocal rule) d d f (x) f (x) dx g(x) − = dx g(x) g(x)2 d d f (x) − f (x) dx g(x) g(x) dx = . g(x)2 ′ ′ Remark: Note that if f (x) and g(x), as well as f (x) and g (x), are continuous, then it follows from the d f (x) quotient rule that dx g(x) is continuous on D f ′ . g Unit 3.4: Derivatives of trigonometric functions 1 lecture Textbook: Section 3.3, pp. 191–197. Learning outcomes: On completion of this unit you should sin h = 1. h 2. be able to prove the formulas for the derivatives of the six trigonometric functions, except sin and cos. 1. know that lim h→0 33 Unit 3.5: The chain rule 2 lectures Textbook: Section 3.4 pp. 199–205. Learning outcomes: On completion of this unit you should 1. know the Chain Rule and be able to use the Chain Rule to find the derivative of a composite function. Additional notes: 1. Study the Chain Rule on page 200 but ignore the comments on the proof (p. 200) and the proof on page 205. 2. Study all the examples except Examples 7 and 9. 3. At this point, also omit Formula 5 for the derivative of b x . 4. Here follows a summary of the Chain Rule formulas: d [ f (x)]n = n[ f (x)]n−1 · f ′ (x) dx d sin f (x) = (cos f (x)) · f ′ (x) (b) dx d (c) cos f (x) = (− sin f (x)) · f ′ (x) dx d (d) tan f (x) = (sec2 f (x)) · f ′ (x) dx d cosec f (x) = (−cosec f (x) cot f (x)) · f ′ (x) (e) dx d (f) sec f (x) = (sec f (x) tan f (x)) · f ′ (x) dx d (g) cot f (x) = (−cosec2 f (x)) · f ′ (x) dx Examples: (a) d sec(x3 ) = sec(x3 ) tan(x3 ) · 3x2 dx ! !6 !5 d 1 −1 1 2 2 2. +x =6 +x + 2x dx x x x2 1. 3. d (x + 1)6 sin4 x = 6(x + 1)5 · sin4 x + (x + 1)6 4 sin3 x cos x dx 4. d (x + 1)6 (sin4 x)6(x + 1)5 − (x + 1)6 4 sin3 x cos x = dx sin4 x sin8 x 34 Unit 3.6: Exponential functions and the number e 1 lecture Source: The notes below and the textbook, sections 1.4 (pp. 45–50) and 3.1 (pp. 179–181). Learning outcomes: On completion of this unit you should be able to 1. explain what the meaning is of a x when x is a natural number, a rational number and an irrational number. 2. write down and use the laws of exponents. 3. find the derivatives of expressions containing e f (x) where f (x) is differentiable. Problems: Exercises 1.4 (p. 52) no. 3, 15, 17, 21, Exercises 3.4 (p. 206) no. 7-55 odd exponential Additional notes: Except for specific references, these notes are a substitute for the textbook, pages 45–50 and 179–181. 1. The domain of f (x) = a x (pp. 45-50) The exponential function f (x) = a x (for a real constant a > 0) is in school defined for positive integers n and rational numbers mn , where n ∈ Z, n > 0 and m ∈ Z, as follows: (a) an = a.a. . . . a(n factors) (b) a−n = 1 an (c) a0 = 1 (d) a /n = x where x ∈ R is such that xn = a 1 (e) am/n = x where x ∈ R is such that xn = am . By the above definition the domain of f (x) = a x includes all the integers (Z) and even all the rational numbers (Q). However, the domain of f (x) = a x can be extended to R. The idea is discussed in the textbook, Section 1.4 (pages 45–47). A rigorous proof can be found in the course notes for the next Calculus module WTW124. The idea is as follows: If x is irrational, then it can be approximated as accurately as we wish by a rational number r. Then ar is an approximation of a x . Consider 2π for 1571 example. Since 3, 142 is an approximation of π, the number 23,142 = 2 500 is an approximation of 15708 2π . The number 23,1416 = 2 5000 is a better approximation. Obviously an even better approximation is possible. 35 Exponential laws and inequalities 2. If a and b are positive real numbers and x and y any real numbers, then (a) a x+y = a x ay ax ay x y (c) (a ) = a xy (b) a x−y = (d) (ab) x = a x b x (e) If a > 1 then ar > a s whenever r > s (f) If 0 < a < 1 then ar < a s whenever r > s The inequalities (e) and (f) above show that f (x) = a x is increasing if a > 1 and decreasing if 0 < a < 1 (see figures 1–6 on pp. 46–48). The derivative of f (x) = a x (a > 0) (pp. 179–181) 3. With respect to the differentiability of the exponential function we have the following theorem: Theorem. Let f (x) = a x (a > 0). If f is differentiable at 0, then f is differentiable everywhere and f ′ (x) = f ′ (0) f (x) for every x ∈ R. Proof. Assume that f is differentiable at x = 0, that is, assume f (0 + h) − f (0) ah − 1 = lim h→0 h→0 h h f ′ (0) = lim exists. Now f (x + h) − f (x) a x+h − a x a x (ah − 1) ah − 1 = lim = lim = a x lim h→0 h→0 h→0 h→0 h h h h f ′ (x) = lim ah − 1 exists, we have that f ′ (x) = f (x) f ′ (0) which shows that h→0 h f ′ (x) exists for every real number x. Since we suppose that f ′ (0) = lim ah − 1 exists for any a > 0. Taking this h→0 h into account, it follows from the above theorem that all the exponential functions is everywhere differentiable with derivative 4. We will assume that the important limit f ′ (0) = lim f ′ (x) = f (x) f ′ (0) for f (x) = a x d x or more explicitly, dx a = f ′ (0)a x for f (x) = a x . Thus it follows for all x that the derivative of any exponential function f at x is proportional to the value of f at x. (The slope of f at x is proportional to f (x).) We will shortly determine f ′ (0), from which it will follow that if 0 < a < 1, then f ′ (0) < 0 if a = 1, then f ′ (0) = 0 if a > 0, then f ′ (0) > 0. 36 (2) The graph of f (x) = a x 5. From items 2e, 2f and (2) above it follows that (a) if a > 1 then f and f ′ are increasing (b) if 0 < a < 1 then f and | f ′ | are decreasing (but f ′ is increasing since f ′′ (x) = f ′ (0)2 a x > 0). Study figures 1–6 on pp. 46–48 and confirm (5a) and (5b) above. The number e 6. A rigorously proof for the fact that the graph of one of the exponential functions f (x) = a x has a ah − 1 slope of 1 at x = 0, that is, f ′ (0) = lim = 1, can be found in the course notes for the next h→0 h Calculus course, WTW124. This is formally stated in the following theorem: eh − 1 = 1. h→0 h Theorem. There exists a number e such that if f (x) = e x , then f ′ (0) = lim It can be proved that e is irrational and that e=1+ 1 1 1 1 + + + + ... 1 2·1 3·2·1 4·3·2·1 (This means that better rational approximations for e are achieved by adding more terms in this “infinite sum”.) d x From the above Theorem it follows that for f (x) = e x we have f ′ (x) = f (x) or e = e x . So, if dx f is a differentiable function, it follows by using the Chain Rule that d f (x) e = f ′ (x)e f (x) . dx Examples: (a) d −x e = −e−x . dx ! 2 d sin2 x sin2 x d 2 (b) e =e sin x = 2esin x sin x cos x. dx dx √ e x d √x e = √ . (c) dx 2 x 37 Unit 3.7: The derivatives of inverse functions 2 lectures Source: The notes below and references to the textbook, sections 1.5 (p. 54–57) and 3.6 (only p. 2222– 223). Learning outcomes: On completion of this unit you should be able to 1. be able to determine the derivatives of inverse functions including those of sin−1 x, tan−1 x and xr when r is rational. Additional notes: The inverse of a function (textbook p. 55) 1. Recall that a function f is called a one-to-one function if it never takes on the same value twice; that is, for every x1 and x2 in the domain of f , if x1 , x2 then f (x1 ) , f (x2 ). 2. Horizontal Line Test. A function is one-to-one if no horizontal line intersects its graph more than once. Examples: (a) y = x2 , x ≥ 0 (b) y = sin x, −π/2 ≤ x ≤ π/2 (c) y = tan x, −π/2 < x < π/2 (d) y = a x , x ∈ R (a > 0). 3. Definition 1. Let f be a one-to-one function with D f = A and R f = B. Then its inverse function f −1 is the function defined by: For every y ∈ B, f −1 (y) = x if and only if f (x) = y. This is the same as f −1 ( f (x)) = x for all x ∈ A and f ( f −1 (y)) = y for all y ∈ B. Therefore D f −1 = B and 38 R f −1 = A. The Differentiability of Inverse Functions 4. The following theorem (which we can’t prove now) tells us when an inverse function is differentiable. Theorem. Let f : D → E be a continuous one-to-one function on an interval I, and let f |I : I → E be the restriction of f on I. That means that f (x) = f |I (x) for all x ∈ D f |I = I. Then (a) R f |I := J is an interval; (b) f |I has a continuous inverse f |−1 I , with D f |−1 = J and R f |−1 = I. I I Also, if f is a one-to-one function that is differentiable at a and f ′ (a) , 0 then f −1 is differentiable at b = f (a). Remark. The formula for the derivative of f −1 (x), if it exists is easily obtained by what is called implicit differentiation: Let g = f −1 . Then f (g(x)) = x for all x ∈ Dg . Therefore d d ( f (g(x)) = x. dx dx By the Chain Rule f ′ (g(x))g′ (x) = 1 that is, g′ (x) = 1 f ′ (g(x)) . The Derivative of arcsin 5. Consider the function f (x) = sin x, − π/2 ≤ x ≤ π/2 . Using the above notation, we can write f (x) as follows f (x) = sin x|[−π/2 ≤x≤π/2 ] . Then f is continuous and strictly increasing and therefore one-to-one on [−π/2 , π/2 ]. Note that D f −1 = [−1, 1] and R f −1 = [−π/2 , π/2 ]. The function f −1 is called arcsin or arcsin . Therefore, y = arcsin x means that sin y = x, y ∈ [−π/2 , π/2 ] and x ∈ [−1, 1]. For example, arcsin(−1/2) = −π/6 since sin(−π/6) = −1/2 and √ √ arcsin(1/ 2) = π/4 since sin π/4 = 1/ 2. 39 6. Theorem. d 1 arcsin x = √ . dx 1 − x2 Proof. The derivative of the inverse function y = arcsin x exists for every x ∈ (−1, 1) since y = sin x is differentiable on (−π/2 , π/2 ). Firstly sin(arcsin x) = x for every x ∈ (−1, 1). Therefore, for every x ∈ (−1, 1) d d sin(arcsin x) = x dx dx d cos(arcsin x) arcsin x = 1 dx d 1 (arcsin x) = . dx cos(arcsin x) But since [cos(arcsin x)]2 + [sin(arcsin x)]2 = 1 and arcsin x ∈ (−π/2 , π/2 ) it follows that cos(arcsin x) > 0 and that cos(arcsin x) = p 1 − [sin(arcsin x)]2 . Finally, 1 d arcsin x = √ . dx 1 − x2 7. In a similar way, you can show cos−1 = arccos? d −1 arccos x = √ . What is the domain and range for dx 1 − x2 8. By the Chain Rule it now follows that if f is differentiable, then d f ′ (x) arcsin( f (x)) = p . dx 1 − ( f (x))2 40 2 2 d 2xe x . Example. arcsin(e x ) = p 2 dx 1 − e2x The Derivative of arctan 9. Consider the function f (x) = tan x, − π/2 < x < π/2 . We can also express f (x) as f (x) = tan x|(−π/2 ,π/2 ) . Then f is continuous and strictly increasing and therefore one-to-one on (−π/2 , π/2 ). Note that for the inverse f −1 , we have D f −1 = (−∞, ∞) and R f −1 = (−π/2 , π/2 ). We refer to f −1 as arctan Therefore, y = arctan x means that tan y = x, y ∈ (−π/2 , π/2 ) and x ∈ (−∞, ∞). √ √ For example, arctan 1 = π/4 since tan π/4 = 1 and arctan(− 3) = −π/3 since tan(−π/3 ) = − 3. d 1 arctan x = . dx 1 + x2 Proof. The derivative of the inverse function y = arctan x exists for every x ∈ (−∞, ∞) since y = tan x is differentiable on (−π/2 , π/2 ). 10. Theorem. Firstly tan(arctan x) = x for every x ∈ (−∞, ∞). Therefore, for every x ∈ (−∞, ∞) d d tan(arctan x) = x dx dx 41 that is, [sec(arctan x)]2 and therefore d arctan x = 1 dx 1 d (arctan x) = . dx [sec(arctan x)]2 But since [sec(arctan x)]2 = 1 + [tan(arctan x)]2 it follows that d 1 . arctan x = dx 1 + x2 11. By the Chain Rule it now follows that if a function f is differentiable, then d f ′ (x) . arctan( f (x)) = dx 1 + ( f (x))2 Example. d sec x tan x . arctan(sec x) = dx 1 + sec2 x 42 The Derivative of xm/n d n 12. We have already proved for a positive integer n that dx x = nxn−1 (see textbook p. 173). d r x = rxr−1 , for r ∈ Q, we need the following result: To proof that dx Lemma. For any non-zero integer n and real number x > 0, d 1 1 1 −1 xn = xn . dx n Proof. For n > 0 the function f (x) = xn is differentiable (we know that f ′ (x) = nxn−1 , see textbook 1 p. 173) and strictly increasing and thus 1 − 1. Thus f −1 (x) = x n is differentiable on (0, ∞). 1 Differentiation of (x n )n = x gives 1 n(x n )n−1 d 1 x n = 1. dx That is d 1/n x = (1/n)x(1/n)−1 . dx Assume now n < 0. Let s = −n. By using the chain rule and the quotient rule we have that d 1 −1 d 1 xn = (x s ) dx dx 1 d 1 = −(x s )−2 x s dx −2 1 1 = −x s x s −1 s 1 − 1 −1 =− x s s 1 1 −1 = xn n (quotient rule) s>0 13. Proposition. For any rational number mn d m/n x = (m/n)x(m/n)−1 . dx Proof. Clearly the proposition is true for mn = 0, since d 0 d x = 1 = 0 = 0x−1 . dx dx m 1 Because x n = (x n )m , the chain rule gives d m d 1 m xn = (x n ) dx dx 1 1 1 = m(x n )m−1 ( )x( n )−1 n m ( m )−( 1 )+( 1 )−1 = ( )x n n n n m ( m )−1 = ( )x n . n 43 Unit 3.8: Implicit differentiation 1 lecture Source: The notes below and references to the textbook, section 3.5 (p. 209). Learning outcomes: On completion of this unit you should be able to 1. be able to use implicit differentiation to find the derivatives of a function that is implicitly defined by an equation in two variables. Additional notes: 1. In the previous unit we were able to find the derivative of a function (y = f −1 (x)) without an explicit formula for the function in terms of x. The crucial point was that we knew that the derivative existed. √ Similarly x2 + y2 = 25 defines one function if y > 0 namely y = 25 − x2 and another function √ 2 if y < 0, namely y = − 25 − x . But without explicitly solving for y in terms of x, there is a theorem that assures one that x2 + y2 = 25 defines functions y = f (x) that are differentiable. The moment one knows that f ′ (x) exists, one differentiates the left hand side and right hand side of x2 + ( f (x))2 = 25 or x2 + y2 = 25 2x + 2 f (x) f ′ (x) = 0 or 2x + 2yy′ = 0 x f (x) or x y′ = − . y to get that is f ′ (x) = − Note that the derivative is expressed in terms of x and y. 2. The textbook does not point out the importance of the fact that one must know that the function is differentiable before one can do implicit differentiation. 44 Unit 3.9: Logarithmic functions and their derivatives 2 lectures Source: The notes below, and references to the textbook, Section 3.6 (p. 217–221). Learning outcomes: On completion of this unit you should be able to 1. know the ln and log laws. 2. write down, use and prove the formulas for the derivatives of y = ln x and y = loga x. 3. differentiate y = a x , y = f (x)g(x) by using the properties of y = ln x. 4. use the technique of logarithmic differentiation. Additional notes: The Logarithmic Function (see also Section 1.5 p. 57–61) 1. Consider the function f (x) = a x , x ∈ (−∞, ∞) and a > 0, a , 1. Then f is continuous and either strictly increasing or strictly decreasing on (−∞, ∞). Note that D f −1 = (0, ∞) and R f −1 = (−∞, ∞). We call f −1 the logarithmic function with base a and denote it by loga x. Therefore, y = loga x means that ay = x, y ∈ (−∞, ∞) and x ∈ (0, ∞). For example, log2 64 = 6 since 26 = 64. Furthermore, since the function y = a x is differentiable on (−∞, ∞), its inverse y = loga x is differentiable on (0, ∞). We will determine the derivative of loga x after the discussion of the so-called natural logarithm. The Natural logarithm 2. The logarithmic function with base e is called the natural logarithm and has a special notation, namely loge x = ln x. Therefore, y = ln x means that ey = x and that ln(e x ) = x, x ∈ (−∞, ∞) and eln x = x, x > 0. We prove the well-known logarithm laws for the natural logarithm and then show how the same laws follow from these. 45 Laws for the natural logarithm 3. For all real numbers a, x, y and with x, y > 0, ln(xy) = ln x + ln y; ln(x/y) = ln x − ln y; ln xa = a ln x. Proof. Let ln x = c and ln y = d. Then x = ec and y = ed and ln xa = ln(ec )a = ln eca = ac = a ln x. Prove the other two laws as an exercise. Change of Base Formula 4. The formula that connects the natural logarithm with the other logarithms: For any real number x > 0, loga x = ln x . ln a Proof. Let loga x = y. Then ay = x and therefore ln x = ln(ay ) = y ln a, that is, y= ln x . ln a General log laws from ln laws 5. For all real numbers a, b, x and y with a, x and y positive, loga (xy) = loga x + loga y; loga (x/y) = loga x − loga y; Proof. ln(xy) ln a ln x + ln y = ln a ln x ln y = + ln a ln a = loga x + loga y. loga (xy) = Prove the other log laws as an exercise. 46 loga (xb ) = b loga x. The derivatives of ln x, ln f (x), loga x and loga f (x) 6. Theorem. d 1 ln x = dx x d f ′ (x) (b) ln f (x) = dx f (x) (a) d 1 loga x = dx x ln a d f ′ (x) (d) loga f (x) = dx f (x) ln a (c) Proof of 6a. Since f (x) = e x is differentiable on R, its inverse f −1 (x) = ln x is differentiable on d 1 d 1 (0, ∞). So, from eln x = x we have eln x ln x = 1. Therefore, ln x = ln x = . dx dx x e Proof of 6b. From the Chain Rule follows that if f is differentiable, then 1 ′ f ′ (x) d ln( f (x)) = f (x) = . dx f (x) f (x) d d ln x 1 d 1 1 loga x = = ln x = · . dx dx ln a ln a dx ln a x 1 d loga f (x) = · f ′ (x). Proof of 6d. From the Chain Rule, dx f (x) ln a Proof of 6c. Logarithmic differentiation 7. Combining the properties of the functions f (x) = e x and f −1 (x) = ln x with the Chain Rule gives a powerful tool to prove the existence of derivatives of power functions and to find them. We call this method logarithmic differentiation. √ d √3 Our first example is the proof that even for irrational powers of x like x 3 it is true that x = dx √ √3−1. 3x d r 8. Theorem. x = rxr−1 for any r ∈ R and x > 0. dx Proof. Since xr > 0 it follows that xr falls in the domain of the function ln x for all x > 0. Since r f (x) = e x and f −1 (x) = ln x are inverse functions, it follows for all x > 0 that xr = eln(x ) and thus that d r d ln x r d r ln x r rxr x = e = e = er ln x = = rxr−1 . dx dx dx x x d 9. Lemma. dx (ln |x|) = 1x . d d Proof. For x > 0 it follows that dx ln |x| = dx ln x = 1x . For x < 0 it follows, by using the chain d d 1 rule, that dx ln |x| = dx ln(−x) = − −x = 1x . 47 10. Examples. 1 √ √ 1 + 2√ √ d d ln(x + x) 2 x+1 x log2 (x + x) = = (a) √ = √ √ . dx dx ln 2 ln 2(x + x) 2 x ln 2(x + x) (b) Since 2 x > 0 for all x, it follows that d ln 2 x d x ln 2 d x 2 = (e ) = e = (ln 2)e x ln 2 = (ln 2)2 x . dx dx dx (c) Since 3sin x > 0 for all x, it follows that d sin x d ln 3 sin x d (ln 3) sin x 3 = (e ) = e = e(ln 3) sin x (ln 3) cos x = 3sin x (ln 3) cos x dx dx dx √ (d) Let f (x) = ( x) x . Since f (x) > 0 for all x ∈ D f , that is for all x > 0, it follows for all x ∈ D f ′ that √ d √ √ √ d √ x d ln √ x x d x ln √ x 1 1 ( x) = (e ) = e = e x ln x x ln x = ( x) x (ln x + x √ · √ ). dx dx dx dx x 2 x (e) Find g′ (x) if g(x) = √ x3 x + 1(x3 + 1)5 . We can determine the g′ (x) using the quotient rule, but this will be quite cumbersome. Instead we use logarithmic differentiation. Let f (x) = ln x. Note that g(x) takes both positive and negative values for different values of x. Hence g(x) does not fall in the domain of f for all x ∈ Dg . The value of the function |g(x)| is bigger than 0 for all non-zero values of x. Thus it follows for all x ∈ Dg , x , 0 that ln |g(x)| = ln √ x3 x + 1(x3 + 1)5 |x|3 = ln √ | x + 1||x3 + 1|5 √ = ln |x|3 − ln x + 1 − ln |x3 + 1|5 1 = 3 ln |x| − ln(x + 1) − 5 ln |x3 + 1|. 2 By differentiating on both sides, it follows that d g′ (x) 3 1 5(3x2 ) ln |g(x)| = = − − 3 . dx g(x) x 2(x + 1) x + 1 Therefore, it follows for all x ∈ Dg′ , x , 0 that g (x) = √ ′ = √ x3 x + 1(x3 + 1)5 3x2 x + 1(x3 + 1)5 3 1 15x2 − − 3 x 2(x + 1) x + 1 − √ x3 x + 1(x3 + 1)5 ! ! 1 15x2 + . 2(x + 1) x3 + 1 Since the derivative of a polynomial, as well as a root function is continuous, it follows that the derivative of g(x) is continuous (see remark after the quotient rule). Thus it follows for all x ∈ Dg′ = Dg (i.e. including x = 0) that ! x3 1 15x2 3x2 ′ g (x) = √ − √ + . x + 1(x3 + 1)5 x + 1(x3 + 1)5 2(x + 1) x3 + 1 48 Unit 3.10: Hyperbolic functions Textbook: Section 3.11, pp. 261–266. Learning outcomes: On completion of this unit you should 1. be able to write down and use the definitions of the hyperbolic functions y = sinh x, y = cosh x and y = tanh x. 2. know, be able to prove and use the derivatives of the functions y = sinh x, y = cosh x and y = tanh x. 3. be able to prove the identities involving sinh and cosh . 49 Theme 4: Applications of Differentiation Unit 4.1: Maximum and minimum values 2 lectures Textbook: Section 4.1, pp. 280–286. Learning outcomes: On completion of this unit you should 1. be able to write down and use the definition of an absolute maximum (global maximum) of a function. 2. be able to write down and use the definition of an absolute minimum (global minimum) of a function. 3. be able to write down and use the definition of a local maximum (relative maximum) of a function. 4. be able to write down and use the definition of a local minimum (relative minimum) of a function. 5. know and be able to apply The Extreme Value Theorem (proof in WTW 220). 6. be able to use Fermat’s Theorem. 7. be able to write down and use the definition of a critical point of a function. 8. be able to find the critical points of a function. 9. be able to use the closed interval method to find the absolute extremes of a continuous function on a closed interval. 10. be able to find the absolute and local extremes of a function if the graph of the function is given. Remark: It is important to remember that if c is a critical point it does not mean that f (c) is a local extreme. You have to use the tests in Unit 4.3 to test whether c is a local extreme. 50 Unit 4.2: The Mean Value Theorem 2 lectures Textbook: Section 4.2, pp. 290–295. Learning outcomes: On completion of this unit you should 1. be able to write down Rolle’s Theorem and apply it. 2. be able to write down the Mean Value Theorem and apply it. 3. know that a function with a zero derivative on an open interval is a constant function on the interval. 4. know and be able to prove that f ′ (x) = g′ (x) for all x in (a, b) implies that f (x) = g(x) + c for all x in (a, b), where c is some constant. (The graph of f is a vertical shift of the graph of g.) Unit 4.3: How the derivative affects the shape of the graph 2 lectures Textbook: Section 4.3, pp. 296–305. Learning outcomes: On completion of this unit you should be able to 1. write down and use the definition of a function that is increasing on an interval. 2. write down and use the definition of a function that is decreasing on an interval. 3. use the Increasing / Decreasing Test. 4. use the First Derivative Test to find the local extremes of a function. 5. write down and use the definition of a function that is concave upward on an interval. 6. write down and use the definition of a function that is concave downward on an interval. 7. apply the Concavity Test. 8. write down and use the definition of an inflection point. 9. use the second derivative to find the inflection point(s) of a function. 10. use the Second Derivative Test to find the local extremes of a function. Remark: Omit Examples 6, 7 and 8 for now. We will do curve sketching in Unit 4.5. 51 Unit 4.4: Indeterminate forms and L’Hospital’s rule 2 lectures Textbook: Section 4.4, pp. 309–316. Learning outcomes: On completion of this unit you should be able to 1. explain what indeterminate limit forms are. 2. write down the different types of indeterminate forms. 3. identify when a limit is of indeterminate form. 4. use the rule of L’Hospital to find certain limits of indeterminate forms. Remark: Use the following notation to indicate indeterminate forms: ex ∞ ex ∞ (form or type ) = lim (form or type ) = . . . x→∞ x2 x→∞ ∞ 2x ∞ Example. lim Unit 4.5: Curve sketching 2 lectures Textbook: Section 4.5, pp. 320–327. Learning outcomes: On completion of this unit you should be able to sketch the graph of a given function. It is a good test of your knowledge and understanding of Themes 3 and 4. Procedure: When we ask you to sketch the graph of a function you have to 1. find the domain of the function. 2. find the x− and y− intercepts of the function. 3. determine whether the function is even, odd, periodic, or none of these. 4. find the horizontal asymptotes of the function. 5. find the vertical asymptotes of the function. 6. find the interval(s) on which the function is increasing and the interval(s) on which the function is decreasing. 7. find the local extremes of the function. (Use number 6.) 8. find the interval(s) on which the function is concave upward and the interval(s) on which the function is concave downward. 9. find the inflection points of the function, and 10. use the information above to sketch the graph of the function. 52 Unit 4.6: Optimization problems 2 lectures Textbook: Section 4.7, pp. 336–342. Learning outcomes: On completion of this unit you should 1. know what is meant by an optimization problem. 2. be able to convert a word problem into a mathematical optimization problem by setting up the function that has to be minimized or maximized. 3. be able to use the methods in this theme to find absolute extreme values. 4. be able to solve optimization problems such as described in the examples. Unit 4.7: Antiderivatives 1 lecture Textbook: Section 4.9, pp. 356–360. Learning outcomes: On completion of this unit you should be able to 1. write down and use the definition of an antiderivative of a function. 2. find the most general antiderivative F of a function f if an antiderivative of f is known. 3. find the function f if an antiderivative of f (x) and, for some a, f (a) are known. Remarks: 1. You can omit the section about linear motion (textbook pp. 360–361). 2. You must be able to explain the table on p. 358. 3. Theorem 1 on page 357 is a reformulation of Corollary 7 on page 294. 53 Theme 5: Integration Unit 5.1: The area problem 1.5 lectures Textbook: Section 5.1, pp. 372–381. Learning outcomes: On completion of this unit you should be able to 1. estimate the area of a region that lies under a curve by using the sum of the areas of rectangles. 2. find an upper and lower estimate of the area of a region that lies under a curve by using the sum of the areas of rectangles. Remarks: Omit the distance problem (p. 379–381). Unit 5.2: The definite integral 2.5 lectures Textbook: Stewart, Section 5.2 pp. 384–394. Learning outcomes: On completion of this unit you should 1. know that the integral has applications other than finding areas. 2. be able to interpret and use the definition of the definite integral. 3. know what the integrand and limits of integration of a definite integral is. 4. be able to use a Riemann sum to approximate a definite integral. 5. know and be able to use the properties of a definite integral. Remark: Omit the Midpoint Rule (p. 390–391) 54 Unit 5.3: The Fundamental Theorem of Calculus 2 lectures Textbook: Section 5.3, pp. 399–405. Learning outcomes: On completion of this unit you should 1. know and be able to use the Fundamental Theorem of Calculus (Part 2). Remarks: 1. Do not read the proof of the Fundamental Theorem of Calculus (Part 2) in the textbook. Read the proof given below. 2. Study Examples 5 to 9 on pp. 403 - 405. Omit the other examples. 3. The Fundamental Theorem of Calculus Part 1 will be treated in WTW124. Fundamental Theorem of Calculus (Part 2): Let f be continuous on [a, b] and differentiable on (a, b), and assume f ′ is integrable on [a, b] then Z b f ′ (x)dx = f (b) − f (a). a Proof. Divide [a, b] into n subintervals of equal length △x = b−a n and let x0 = a, x1 , x2 , . . . , xn = b be the endpoints of the subintervals. Note that f (b) − f (a) = n X [ f (xk ) − f (xk−1 )] (1) k=1 Now, f is continuous on each interval [xk−1 , xk ], and differentiable on each interval (xk−1 , xk ), for k = 1, 2, . . . , n. By the Mean Value Theorem f (xk ) − f (xk−1 ) = f ′ (ck ) △ x (2) for some ck ∈ (xk−1 , xk ). Thus by (1) and (2) we obtain n X f (b) − f (a) = [ f (xk ) − f (xk−1 )] = k=1 n X f ′ (ck ) △ x. k=1 Taking limits both sides as n → ∞, using the ck ’s as sample points in [xk−1 , xk ] and using the fact that f ′ is integrable on [a, b], we have Z b f (x)dx = lim ′ a n→∞ n X f ′ (ck ) △ x = lim [ f (b) − f (a)] = f (b) − f (a), n→∞ k=1 since f (b) − f (a) is constant and by definition Z b a f ′ (x)dx = lim n→∞ exists. 55 n X k=1 f ′ (ck ) △ x Unit 5.4: Indefinite integrals 1 lecture Textbook: Section 5.4, pp. 409–415. Learning outcomes: On completion of this unit you should Z 1. know that the notation f (x) dx is traditionally used for an antiderivative of f. Z 2. know that f (x) dx represents an infinite number of functions all differing by a constant. Z b 3. know that f (x) dx is a real number and not an antiderivative. a 4. be able to evaluate indefinite integrals. Remarks: 1. The tables in the textbook p. 358 and p. 410 are essentially the same. 2. Omit the section on The Net Change Theorem, pages 412–415. Z Additional notes: Consider 2x cos(x2 ) dx. By the Chain Rule d sin(x2 ) = cos(x2 )2x dx and therefore Z 2x cos(x2 )dx = sin(x2 ) + c. In general, if F is an antiderivative of f, then Z g′ (x) f (g(x)) dx = F(g(x)) + c since d [F(g(x)) + c] = F ′ (g(x))g′ (x) = f (g(x))g′ (x). dx Here are a number of examples to illustrate the previous remark: Z | f (x)]n+1 1. [ f (x)]n f ′ (x) dx = + c in case n , −1 n+1 Z ′ f (x) 2. /, dx = ln | f (x)| + c f (x) Z 3. f ′ (x) cos f (x) dx = sin f (x) + c Z f ′ (x) sin f (x) dx = − cos f (x) + c Z f ′ (x) sec2 f (x) dx = tan f (x) + c 4. 5. 56 Z f ′ (x) sec f (x) tan f (x) dx = sec f (x) + c Z f ′ (x) sinh f (x) dx = cosh f (x) + c Z f ′ (x) cosh f (x) dx = sinh f (x) + c Z f ′ (x) dx = arcsin f (x) + c p 1 − [ f (x)]2 Z f ′ (x) dx = arctan f (x) + c 1 + [ f (x)]2 Z f ′ (x) dx = sinh−1 f (x) + c p 2 1 + [ f (x)] 6. 7. 8. 9. 10. 11. Unit 5.5: Transformation of the integral 3 lectures Textbook: Section 5.5, pp. 419–425. Learning outcomes: On completion of this unit you should 1. be able to use the Substitution Rule for indefinite integrals. 2. know and apply the Transformation Theorem (substitution rule for definite integrals). 3. know and apply the theorem about “Integrals of Symmetric Functions”. Remark: Take care to also transform the bounds of integration when using the Transformation Theorem (substitution rule) for definite integrals. 57 Appendix I: Differentiation formulas 1. Derivative of a constant function d c = 0, c ∈ R dx 2. Derivative of a power function d d n x = nxn−1 and [ f (x)]n = n[ f (x)]n−1 f ′ (x) for every real number n dx dx 3. Derivative of the natural exponential function d x d f (x) e = e x and e = e f (x) f ′ (x) dx dx 4. Derivative of any exponential function d x d f (x) a = (ln a)a x and a = (ln a)a f (x) f ′ (x), a > 0 dx dx 5. The derivatives of the trigonometric functions d d sin x = cos x and sin f (x) = cos f (x) × f ′ (x) dx dx d d cos x = − sin x and cos f (x) = − sin f (x) × f ′ (x) dx dx d d tan x = sec2 x and tan f (x) = sec2 f (x) × f ′ (x) dx dx d d cosecx = −cosecx × cot x and cosec f (x) = −cosec f (x) × cot f (x) × f ′ (x) dx dx d d sec x = sec x × tan x and sec f (x) = sec f (x) × tan f (x) × f ′ (x) dx dx d d cot x = −cosec2 x and cot f (x) = −cosec2 f (x) × f ′ (x) dx dx 6. The derivatives of the inverse trigonometric functions d d 1 arcsin x = sin−1 (x) = √ dx dx 1 − x2 1 d d arctan x = tan−1 (x) = dx dx 1 + x2 and and 7. The derivative of logarithmic functions d 1 d f ′ (x) ln x = , x > 0 and ln f (x) = dx x dx f (x) d 1 loga x = , x>0 dx x ln a 8. The derivatives of the hyperbolic functions d sinh x = cosh x dx d cosh x = sinh x dx d tanh x = sec h2 x dx 58 d f ′ (x) arcsin f (x) = p dx 1 − [ f (x)]2 d f ′ (x) arctan f (x) = dx 1 + [ f (x)]2 Appendix II: Differentiation rules Assume the functions are differentiable. Derivative of a constant multiple d d [c f (x)] = c[ f (x)] dx dx Sum Rule " # " # d d d [ f (x) + g(x)] = f (x) + g(x) dx dx dx Difference Rule " # " # d d d [ f (x) − g(x)] = f (x) − g(x) dx dx dx Product Rule " # " # d d d [ f (x) × g(x)] = f (x) × g(x) + f (x) × g(x) dx dx dx Quotient Rule " # d g(x)] [ d f (x)] × g(x) − f (x) × [ dx d f (x) = dx 2 dx g(x) [g(x)] The Chain Rule d d ( f ◦ g)(x) = f (g(x)) × g′ (x) dx dx In Leibniz notation: If y = f (u) and u = g(x) then dy dy du = × dx du dx 59 Appendix III: List of standard indefinite integrals 1. Integral of a constant function Z c dx = cx + C, c ∈ R 2. Integral of a power function Z Z 1 1 n+1 x + C and [ f (x)]n f ′ (x)dx = [ f (x)]n+1 + C for each real number xn dx = n+1 n+1 n , −1 3. Integral of the natural exponential function Z Z x x e dx = e + C and e f (x) f ′ (x)dx = e f (x) + C 4. Integral of any exponential function Z Z 1 x 1 f (x) a x dx = a + C and a f (x) f ′ (x)dx = a + C, a > 0 ln a ln a 5. The integrals of the trigonometric functions Z Z sin xdx = − cos x + C and sin( f (x)) f ′ (x))dx = − cos( f (x)) + C Z Z cos xdx = sin x + C and cos( f (x)) f ′ (x)dx = sin( f (x)) + C Z Z sec2 xdx = tan x + C and sec2 ( f (x)) f ′ (x)dx = tan( f (x)) + C Z Z cosecx cot xdx = −cosecx + C and cosec( f (x)) cot( f (x)) f ′ (x)dx = −cosec( f (x)) + C Z Z sec x tan xdx = sec x + C and sec( f (x)) tan( f (x)) f ′ (x)dx = sec( f (x)) + C Z Z cosec2 xdx = − cot x + C and cosec2 ( f (x)) f ′ (x)dx = − cot( f (x)) + C 6. The integrals of the inverse trigonometric functions Z 1 dx = arcsin(x) + C = sin−1 (x) + C √ 2 1−x Z f ′ (x) dx = arcsin( f (x)) + C = sin−1 ( f (x)) + C p 2 1 − [ f (x)] Z 1 dx = arctan(x) + C = tan−1 (x) + C 1 + x2 Z f ′ (x) dx = arctan( f (x)) + C = tan−1 ( f (x)) + C 1 + [ f (x)]2 7. The integrals of logarithmic functions Z Z ′ 1 f (x) dx = ln |x| + C and dx = ln | f (x)| + C x f (x) 60 8. The integrals of hyperbolic functions Z Z sinh xdx = cosh x + C and sin h( f (x)) f ′ (x)dx = cosh( f (x)) + C Z Z cosh xdx = sinh x + C sec h xdx = tanh x + C 2 Z cos h( f (x)) f ′ (x)dx = sinh( f (x)) + C Z sec h2 ( f (x)) f ′ (x)dx = tanh( f (x)) + C and and 61 FLY@UP encourages students to make use of the available UP resources in order to finish their degrees in the shortest possible time. Think carefully before dropping modules (after the closing date for amendments or cancellation of modules). Make responsible choices with your time and work consistently. Aim for a good semester mark. 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