4 EVALUATING AND PERFORMING OPERATIONS ON FUNCTIONS for General Mathematics Senior High School (CORE) Quarter 1 / Week 1 1 FOREWORD This Self-Learning Kit for General Mathematics is designed specifically for Grade 11 students in the Senior High School. Thus, a modest background in grade school mathematics is important, written in a precise, readable, and conventional manner to facilitate students’ understanding of the subject. It is aligned with the BEC of the Department of Education following the prescribed MELCs (Most Essential Learning Competencies. It has the following features proven to be valuable aids to learning Mathematics even at home. What happened This section contains pre-activities like review of the prior knowledge and a pretest on what the learners have learned in their previous discussions. What I Need to Know (Discussion) This section contains definition of terms, different examples of real-life situations as application of functions. It gives examples and the corresponding situations that clearly illustrate the applicability of a mathematical concept. What I have Learned (Evaluation/Post Test) The exercises contained in this section are guaranteed to build mathematical comprehension, skills, and competence. These serve as a diagnostic tool to identify the learners’ areas of strengths and difficulties. 2 OBJECTIVES At the end of the lesson, the learners are expected to: K: represent real-life situations using functions, including piecewise; S: evaluate and perform operations on functions; and A: appreciate the use of functions to real-life situations. LESSON 1 REPRESENTING REAL-LIFE SITUATIONS USING FUNCTIONS I. WHAT HAPPENED PRE-TEST: Instruction: Read each statement carefully then choose the letter of the best answer. Write your answer in your notebook. 1. What do we call the elements of x or inputs of functions? A. Domain B. relation C. range D. none of them 2. What do we call the elements of y or outputs of functions? A. domain B. relation C. range D. none of them 3. In a given relation below, what is the range? A. {4,5,6} B. {−2,3} C. {−2,4,6} D. none of them 4. Which of the following is not a function? A. {(0,1), (1,2), (2,3), (3,4)} C. {(1,3), (4,2), (2,0), (3,4)} B. {(0,2), (1,3), (4,3), (1,2)} D. {{1,2}, {2,2}, {3,2}, {4,2}} 5. Among the value of x and y, which is independent variable? A. x variable B. y variable C. x and y variable D. none of them II. WHAT YOU NEED TO KNOW 3 This image is a visual representation of function because they have an input, process, and output. DISCUSSION What is a function? Definition of Functions • • • • It is a set of ordered pairs of elements x variable and y variable where the first element x is not repeating. It is a set of ordered pairs of elements x and y variables where the second element y is repeating, or it is called many to one function. Every value of x corresponds to a unique value of y it is called one to one function. If every value of x corresponds two or more value of y which is called relation not a function because function has no element of x is repeating. Note: All functions are a relation but not all relations are functions. Functions as representations of real-life situations Identifying an appropriate function will lead to a better understanding of various phenomena. Example 1: Give a function C that can represent the cost of buying x meals if one meal costs β±40. Solution: Since each meal cost β±40, then the cost of function is πΆ (π₯ ) = 40π₯ Example 2: One hundred meters of fencing is available to enclose a rectangular area next to a river (see illustration below). Give a function A that can represent the area that can be enclose, in terms of x. Solution: The area of a rectangular enclosure is π΄ = π₯π¦. Write this as a function of π₯. Since only 100 m of fencing is available, then the steps are as follows. A. Write the equation π₯ + 2π¦ = 100 B. Find π¦? C. Simplify the equation π₯ + 2π¦ = 100 2π¦ = 100 − π₯; {π‘ππππ πππ ππ‘πππ πππ‘βππ } 4 π¦ = 50 − .5π₯ Since the equation A= xy, substitute the value of π¦ = 50 − .5π₯ to A=xy π΄ = π₯(50 − .5π₯ ); {π πππππππ¦ π’π πππ πππ π‘ππππ’π‘ππ£π πππππππ‘π¦ ππ πππ’ππππ‘π¦} π΄ = 50π₯ −. 5π₯ 2 ; {πππ‘ππππππ‘ π΄ ππ ππ’πππ‘πππ π΄(π₯)} π΄ = 50π₯ −. 5π₯ 2 What is Piecewise Function? A piece-wise function consists of a set of different intervals of x with the value of y. Some situations can only be described by more than one formula, depending on the value of the independent variable. Example 1: A user is chargeβ±300 monthly for a mobile plan, which includes 100 free text messages. Messages more than 100 are charged β±1 each. Represent the amount of a consumer pays each month as a function of the number of messages m sent in a month. Solution: Let π‘(π) represent the amount paid by the consumer each month. It can be expressed by the piece-wise function. π‘(π) = { ππ 0 < π ≤ 100 ππ > 100 300 300 + π Example 2: A jeepney ride cost β±8 for the first 4km, and each additional integer kilometer adds β±1.50 to the fare. Use a piecewise function to represent the jeepney fare in terms of the distance d in kilometer. Solution: The input value is distance, and the output is the cost of the jeepney fare. If π(π ) represents the far as a function of distance, the function can be represented as follows: ππ 0 < π ≤ 4 ππ π > 4 8 πΉ (π ) = { 8 + 1.5π III. WHAT HAVE I LEARNED POST TEST Read and answer the following problems. Answer in your notebook. 1. A videoke machine can be rented for β±1000 for three days, but for the fourth day onwards and additional cost of β±400 per day is added. Represent the cost of renting a videoke machine as a piecewise function. 2. The fee for hiring a guide to explore a cave is β±700. A guide can only take care of a maximum of 4 persons, and additional guides can be hired as needed. Represent the cost of hiring guides as a function of the number of tourists who wish to explore the cave. 3. The cost of hiring a catering service to serve food for a party is β±150 per head for 20 persons or less, β±130 per head for 21 to 50 persons, and β±110 per head for 51 to 100 persons. For 100 or more persons, the cost is at β±100 per head. Represent the total cost as piecewise function of the number of attendees of the party. 5 4. A courier company charges β±100 per package weighing 2kg or less. They charge β±15 for each additional kilogram or fraction of a kilogram up to 5 kg. Write a piecewise function that gives the cost C for shipping a package weighing k kilograms. 5. Elaine is paying β±799 for an internet service with 3GB monthly data and a connection fee of β±20 per hour more than the data. Represent her monthly bill as a function of connection time. LESSON 2 EVALUATING FUNCTIONS I. WHAT HAPPENED Review: PEMDAS (Parenthesis, Exponent, Multiplication, Division, Addition, Subtraction) Example: 4(2 − 3)2 − 8 ÷ 2π₯3 + 1 Grouping Symbols 4(−1)2 − 8 ÷ 2 × 3 + 1 Exponents π ( π) − π ÷ π × π + π Multiplication and Division {whichever comes first} π−π÷π×π+π π−π×π+π π − ππ + π Addition and Subtraction {whichever comes first} −8 + 1 −7 PRE-TEST Instructions: Evaluate the following functions at π₯ = 1.5. Answer in your activity notebook/sheets. a. b. c. d. π(π₯ ) = 2π₯ + 1 π(π₯ ) = π₯ 2 − 2π₯ + 2 π(π₯ ) = √π₯ + 1 2π₯+1 π (π₯ ) = π₯−1 II. WHAT YOU NEED TO KNOW DISCUSSION: Evaluating functions means replacing the variable in the function, in this case π₯, with a value from the function’s domain and computing for the result. To denote that we are evaluating of π₯ for some π₯ in the domain of f, write π (π₯ ). Example 1. Evaluate the function π(π₯) = 2π₯ 2 − 3π₯ + 2 when π₯ = −1. 6 Solution: Step 1: Write the original function. π (π₯ ) = 2π₯ 2 − 3π₯ + 2 Step 2: Substitute the given value to the variable. π (−1) = 2(−1)2 − 3(−1) + 2 Step 3: Simplify by applying the order of operations. π (−1) = 2(1) + 3 + 2 π (−1) = 2 + 3 + 2 π (−1) = 7 Example 2. Find π(−4) and π(1) where π and π are as defined in π (π₯ ) = 2π₯ + 1. Solution: This is not possible because −4 is not the domain of π(π₯) and 1 is not in the domain of π(π₯). Example 3. Evaluate the following functions, where π (π₯ ) = 2π₯ + 1 and π(π₯ ) = π₯ 2 − 2π₯ + 2. a. π(3π₯ − 1) b. π(2π₯ + 3) Solution: a. To evaluate π (3π₯ − 1), {πππππππ πππ π‘βπ π₯ ππ π (π₯ ) = 2π₯ + 1 ππ¦ 3π₯ − 1} π (3π₯ − 1) = 2(3π₯ − 1) + 1 ; {πππππ¦ πππ π‘ππππ’π‘ππ£π πππππππ‘π¦ ππ πππ’ππππ‘π¦} = 6π₯ − 2 + 1; {πππππ¦ πππππ‘πππ ππ π’πππππ π ππππ } π (3π₯ − 1) = 6π₯ − 1 b. To evaluate π(2π₯ + 3); {πππππππ πππ π₯ ππ π(π₯ ) = π₯ 2 − 2π₯ + 2 ππ¦ 2π₯ + 3} π(2π₯ + 3) = (2π₯ + 3)2 − 2(2π₯ + 3) + 2 note: {apply square of binomials and distributive property} = (4π₯ 2 + 12π₯ + 9) − 4π₯ − 6 + 2{πππππππ ππππ π‘ππππ } π(2π₯ + 3) = 4π₯ 2 + 8π₯ + 5 III. WHAT HAVE I LEARNED POSTTEST A. Instruction: Answer the following given activities in your notebook. 1. Given π(π₯) = π₯ − 2, find the following values. π. π (0) b. π (3) c. π (−1) 4 2. Given π(π₯ ) = π₯, find the following values. a. π(1) b. π (2) c. π(−1) d. π(√2) 1 e. π (1−π₯) 7 OPERATIONS ON FUNCTIONS LESSON 3 I. WHAT HAPPENED QUICK REVIEW *Adding, subtracting and multiplying two or more functions together will result in another function. Dividing two functions together will result in another function if the denominator or divisor is not the zero function. PRE-TEST Perform the indicated operation: 3 6 6 5π₯ 1. 4 + 5 = 4. π₯ ÷ 3 = 2. 3. 6 7 5 − = 2 5. 2 2π₯−1 π₯ 2 −4 π₯+2 β 2π₯−1 = 1 + π₯−3 = π₯+7 II. WHAT YOU NEED TO KNOW DISCUSSION Function Operations: Definition. Let f and g be functions. (a) Their sum, denoted by f + g, is the function defined by (π + π)(π) = π(π) + π(π) Let π(π) = π + π and π(π) = ππ + ππ – π Example 1. Determine the function (π + π)(π₯). Solution. (π + π)(π₯) = π(π₯) + π(π₯) by definition 2 = π₯ + 3 + π₯ + 2π₯ – 8 by substitution 2 = π₯ + 3π₯ – 5 by combining like terms (b) Their difference, denoted by f – g, is the function defined by (π – π)(π) = π(π) – π(π) Example 2. Determine the function (π – π)(π₯). Solution. (π – π)(π₯) = π(π₯) – π(π₯) 8 by definition = π₯ + 3 – ( π₯ 2 + 2π₯ – 8) = π₯ + 3 – π₯ 2 – 2π₯ + 8 = −π₯ 2 − π₯ + 11 (c) by substitution by distributive property by combining like terms Their product, denoted by f β g, is the function defined by (π β π)(π) = π(π) β π(π) Example 3. Determine the function (π β π)(π₯). Solution. (π β π)(π₯) = π(π₯) β π(π₯) = (π₯ + 3) β ( π₯ 2 + 2π₯ – 8) = π₯(π₯ 2 + 2π₯ – 8) + 3( π₯ 2 + 2π₯ – 8) = π₯ 3 + 2π₯ 2 – 8π₯ + 3π₯2 + 6π₯ – 24 = π₯ 3 + 5π₯ 2 – 2π₯ – 24 (d) by definition by substitution by distributive property by distributive property by combining like terms Their quotient, denoted by f/g, is the function defined by π π(π) ( ) (π ) = ππ (f/g)(π) = π(π)/π(π), excluding the values of x π(π) π where g(x) = 0. π Example 4. Determine the function (π) (π₯). π ( π ) (π₯) = Solution. = = (e) π(π) by definition π(π) (π₯ + 3) by substitution ( π₯ 2 + 2π₯ – 8) (π₯ + 3) by factoring ( π₯ +4)(π₯ – 2) The composite function, denoted by (π β¦ π), is defined by (π β¦ π)(π) = π(π(π)) Example 5. Find and simplify (π β¦ π)(π₯). Solution. (π β¦ π)(π₯) = π(π(π₯)) = π(π₯) + 3 = π₯ 2 + 2π₯ – 8 + 3 = π₯ 2 + 2π₯ – 5 by definition g(x) is the input of f(x) by substitution by combining like terms ILLUSTRATIVE EXAMPLES Example 1. Consider the following functions below: π (π₯ ) = π₯ + 3 π(π₯ ) = 2π₯ − 7 Determine the following. a) (π + π)(π₯) b) (π/β)(π₯) Solution. π(π₯ ) = π₯ 2 + 2π₯ − 8 π₯+7 β (π₯ ) = 2−π₯ c) (π – β)(π₯) d) (π β π)(π₯) 9 e) (π β¦ π)(π₯) a) (f + p)(x) = f(x) + p(x) = x + 3 + 2x – 7 = 3x – 4 by definition by substitution combining like terms b) (p/h)(x) = p(x)/h(x) 2π₯−7 = π₯+7 by definition by substitution 2−π₯ = 2π₯ − 7 β step 1 for the operation division π₯+7 4π₯−2π₯ 2 −14+7π₯ = = 2−π₯ by distributive property π₯+7 −2π₯ 2 +11π₯−14 combining like terms π₯+7 c) (π – β)(π₯) = π(π₯) – β(π₯) π₯+7 = 2π₯ − 7 − 2−π₯ by definition by substitution 2−π₯ π₯+7 = (2π₯ − 7) β 2−π₯ − = = = = 4π₯−2π₯ 2 −14+7π₯ − step 2 of the operation subtraction 2−π₯ π₯+7 by distributive property 2−π₯ 2−π₯ 4π₯−2π₯ 2 −14+7π₯−(π₯+7) subtracting two same denominators 2−π₯ 4π₯−2π₯ 2 −14+7π₯− π₯−7 by distributive property 2−π₯ −2π₯ 2 +10π₯−21 simplifying the numerator 2−π₯ d) (π β π)(π₯) = π(π₯) β π(π₯) = (π₯ + 3)(π₯ 2 + 2π₯ − 8) = π₯ 3 + 2π₯ 2 − 8π₯ + 3π₯ 2 + 6π₯ − 24 = π₯ 3 + 5π₯ 2 − 2π₯ − 24 e) (π β¦ π)(π₯) = π(π(π₯)) = π(π₯) + 3 = π₯ 2 + 2π₯ − 8 + 3 = π₯ 2 + 2π₯ − 5 by definition by substitution by distributive property combining like terms by definition g(x) is the input of f(x) by substitution combining like terms Example 2. Each pair of functions below have a special relationship because π₯ 2π₯ (f β¦ g)(x) = x and (g β¦ f)(x) = x. Verify these π(π₯ ) = π₯−2 ; π(π₯ ) = π₯−1 Solution. (f β¦ g)(x) = f(g(x)) = π(π₯) π(π₯)−2 = 2π₯ π₯−1 2π₯ −2 π₯−1 10 = 2π₯ π₯−1 2π₯−2(π₯−1) π₯−1 = 2π₯ π₯−1 2π₯−2π₯+2 π₯−1 = 2π₯ π₯−1 2 π₯−1 2π₯ =π₯−1 β (g β¦ f)(x) = g(f(x)) = π₯−1 2 2π(π₯) π(π₯)−1 2π₯ = π₯−2 β π₯−2 2 =x = π₯ ) π₯−2 π₯ −1 π₯−2 2( = 2π₯ π₯−2 π₯−1(π₯−2) π₯−2 = =x III. WHAT HAVE I LEARNED POST TEST: Find and simplify the following functions given f(x) and g(x): 1. f(x) = x + 2 ; g(x) = x2 – 4 (f + g)(x) = 2. π (π₯ ) = √(π₯ − 2)2 ; g(x) = x2 – 4 (g/f)(x) = 3. π (π₯ ) = π₯−2 π₯+2 ; π (π₯ ) = (f β g)(x) = 4 4. π (π₯ ) = π₯+3; π(π₯ ) = (f – g)(x) = 1 π₯ 2 π₯+3 5. f(x) = x2 – 2x + 1 ; g(x) = x + 2 (f β¦ g)(x) = 11 2π₯ π₯−2 π₯−π₯+2 π₯−2 = 2π₯ π₯−2 2 π₯−2 SYNOPSIS This Self Learning Kit (SLK) discusses on how to represent real-life situations using functions, evaluate functions and perform operations on functions. . It also gives examples in solving problems involving functions. The learners are expected to assess their skills and apply what they have learned in their everyday life. It also enhances their skills and utilizes what they have learned. Bring it on and let us discover jointly in this wonderful journey of learning how to perform operations on functions including composition of functions. WRITERS RONALD G. TOLENTINO is a faculty member of Negros Oriental High School (NOHS- SHS Department). He finished his BS Mathematics degree batch 1993 and earned his 27 units in MATMathematics from Silliman University. He graduated the CPE at PTC Dumaguete City last 2018. He is currently the SHS DRRR Coordinator of Negros Oriental High School. 12 ANSWER KEY LESSON 1 LESSON 3 Pre-Test 39 23 3π₯+1 1. 20 2. − 14 3. (π₯+7)(π₯−3) Pre-test 1. A 2. C 3. C 4. B 5. A Posttest 1000 ππ 0 ≤ π₯ ≤ 3 1. π (π₯ ) = { 1000 + 400(π₯ − 3) ππ π₯ ≥ 4 18 4. 5π₯ 2 Posttest π₯ 2. π(π₯ ) = 700 (4) , π₯ ∈ π 150π₯ ππ 0 ≤ π₯ ≤ 20 130π₯ ππ 21 ≤ π₯ ≤ 50 3. π (π₯ ) = { 110π₯ ππ 51 ≤ π₯ ≤ 100 100π₯ ππ π₯ ≥ 100 100 ππ 0 < π₯ ≤ 2 115 ππ 2 < π₯ ≤ 3 4. π (π₯ ) = { 130 ππ 3 < π₯ ≤ 4 145 ππ 4 < π₯ ≤ 5 5. π (π₯ ) = 799 + 20π₯ 1. π₯ 2 + π₯ − 2 3. 5. π₯ 2 + 2π₯ + 1 LESSON 2 Pre-test a. π(π₯ ) = 4 b. π (π₯ ) = 1.25 c. π(π₯ ) = √2.5 d. π (π₯ ) = 8 Posttest 1. a. π (0) = 2 b. π (3) = 1 c. π (−1) = −3 2. a. π (1) = 4 b. π (2) = 2 c. π (−1) = −4 d. π(√2) = π₯−2 π₯(π₯+2) 4√2 2 1 e. π (1−π₯) = 4 − 4π₯ 13 2. π₯ + 2 4. 2 π₯+3 5. π₯ − 2 DEPARTMENT OF EDUCATION SCHOOLS DIVISION OF NEGROS ORIENTAL SENEN PRISCILLO P. PAULIN, CESO V Schools Division Superintendent JOELYZA M. ARCILLA, EdD Assistant Schools Division Superintendent MARCELO K. PALISPIS, EdD Assistant Schools Division Superintendent NILITA L. RAGAY, EdD OIC - Assistant Schools Division Superintendent CID Chief ROSELA R. ABIERA Education Program Supervisor – (LRMS) ELISA L. BAGUIO, EdD Division Education Program Supervisor – MATHEMATICS MARICEL S. RASID Librarian II (LRMDS) ELMAR L. CABRERA PDO II (LRMDS) NAME OF WRITER DOMINADOR A. JUMAO-AS RONALD G. TOLENTINO NAME OF ILLUSTRATOR/LAY-OUT ARTIST/TYPESETTER LITTIE BETH S. BERNADEZ _________________________________ ALPHA QA TEAM LITTIE BETH S. BERNADEZ MERCYDITHA D. ENOLPE RONALD TOLENTINO DIDITH T. YAP BETA QA TEAM ELIZABETH A. ALAP-AP EPIFANIA Q. CUEVAS NIDA BARBARA S. SUASIN VRENDIE P. SYGACO MELBA S. TUMARONG HANNAHLY I. UMALI DISCLAIMER The information, activities and assessments used in this material are designed to provide accessible learning modality to the teachers and learners of the Division of Negros Oriental. The contents of this module are carefully researched, chosen, and evaluated to comply with the set learning competencies. The writers and evaluator were clearly instructed to give credits to information and illustrations used to substantiate this material. All content is subject to copyright and may not be reproduced in any form without expressed written consent from the division.