Construct and compare linear, quadratic, and exponential models and solve problems.
1. Distinguish between situations that can be modeled with linear functions and with exponential functions. a. Prove that linear functions grow by equal differences over equal intervals, and that exponential functions grow by equal factors over equal intervals. b. Recognize situations in which one quantity changes at a constant rate per unit interval relative to another. c. Recognize situations in which a quantity grows or decays by a constant percent rate per unit interval relative to another.
Overview of Lesson
- activate prior knowledge
- present vocabulary and/or big ideas associated with the lesson
- connect assessment practices with curriculum
- model an assessment problem and solution strategy
- facilitate guided practice of student activity
- facilitate a summary and share out of student work
Optional: Provide additional problem sets
Optional HW - Write the math assignment.
If the graph is a straight If the graph is a parabola, the line, the function is in the function is in the family of family of linear functions.
quadratic functions .
All first degree functions are linear functions, except
All quadratic functions have an exponent of 2 or can be those lines that are vertical. factored into a single factor
All linear functions can be with an exponent of 2. expressed as , Examples: where m is a constant defined slope and b is the y-intercept.
If the graph is a curve that approached a horizontal limit on one end and gets steeper on the other end, the function is in the family of exponential functions .
An exponential function is a function that contains a variable for an exponent.
Example: y

2 x
Exponential growth and decay can be modeled using the general formula

NOTE: All functions in the form of y
 ax n
, where a

0 and n

1 and n is an odd number , take the form of parabolas.
The larger the value of n , the wider the flat part at the bottom/top.
NOTE: All functions in the form of y
 ax n
, where a

0 and n

1 and n is an even number , take the form of hyperbolas. These are not quadratic functions.
1. Which situation could be modeled by using a linear function? a. a bank account balance that grows at a rate c. the cost of cell phone service that charges of 5% per year, compounded annually b. a population of bacteria that doubles every
4.5 hours a base amount plus 20 cents per minute d. the concentration of medicine in a person’s body that decays by a factor of one-third every hour
2. Which table of values represents a linear relationship? a. c. b. d.
3. The table below shows the average yearly balance in a savings account where interest is compounded annually.
No money is deposited or withdrawn after the initial amount is deposited.

Which type of function best models the given data? a. linear function with a negative rate of change c. exponential decay function b. linear function with a positive rate of change d. exponential growth function

1. ANS: C
Strategy: Eliminate wrong answers. a) Eliminate answer choice a because it describes exponential growth of money in a bank account. b) Eliminate answer choice b because is describes exponential growth of bacteria. c) Choose answer choice c because it can be modeled using the slope intercept formula as follows: d) Eliminate answer choice d because it describes exponential decay of medicine in the body.
PTS: 2 REF: 081412a1 NAT: F.LE.1b TOP: Families of Functions
2. ANS: C
Strategy: Use (the slope formula) to determine which table represents a constant rate of change. A linear function will have a constant rate of change.
Answer Choice First set of coordinates Second set of coordinates a eliminate because slope is not constant
(1,1) and (2,6) (2,6) and (3, 13) b eliminate because slope is not constant
(1,2) and (2,4) (2,4) and (3, 8) choose because c slope is constant
(1,1) and (2,3) (2,3) and (3, 5)
(2,8) and (3, 27) d eliminate because slope is not constant
(1,1) and (2,8)
PTS: 2 REF: 011505a1 NAT: F.LE.1b TOP: Families of Functions
3. ANS: D
Strategy: Input the table into the stats editor of a graphing calculator, then plot the points and examine the shape of the scatterplot.
The data in this table creates a scatterplot that appears to model an exponential growth function.
DIMS? Does It Make Sense? Yes. Savings accounts are excellent exemplars of exponential growth.
PTS: 2 REF: 061406a1 NAT: F.LE.1c TOP: Modeling Exponential Equations

START
PART 1.
PART 2.
PART 3.
PART 4.
PART 5.
PART 6.
Standard “Writing the Math” Assignment
Write your name, date, topic of lesson, and class on your paper.
Copy the problem from the lesson and underline/highlight key words.
State your understanding of what the problem is asking .
Answer the problem.
Explanation of strategy .
Create a new problem that addresses the same mathematical understandings.
State the answer to your new problem .
Clearly label each of the six parts.
Grading Rubric
Each homework writing assignment is graded using a four-point rubric, as follows:
Part 1. Statement of the problem. 1
point is awarded for correctly restating the
2 original problem.
Part 2. Statement of what the problem is really asking.
1
point is awarded for correctly identifying
2 what the problem is asking you to find or do.
Part 3. Solution to the problem. 1
point is awarded for a correct solution to
2 the problem.
Part 4. Written analysis of the mathematics and solution strategy involved in the problem.
Up to 1 point is awarded for an explanation of the mathematics and solution strategy involved in the problem.
Part 5. An alternative version of the problem. Up to 1 point is awarded for creating a new problem that involves similar mathematics and a similar solution strategy.
Part 6. Solution to the alternative version of the problem.
1
point is awarded for correctly solving the
2 new problem that you have created.
This assignment/activity is designed to incorporate elements of
Polya’s four step universal algorithm
for problem solving with the idea that writing is thinking.
Rationale for Assignment
Each New York Regents Algebra I (Common Core) examination contains 13 open response problems. An analysis of the first three Algebra I examinations revealed that approximately 51% (20 out of 39) of these open response problems instructed students to: 1) describe; 2) state ; 2) explain; 3) justify or otherwise write about their answers.
It is theorized that students can benefit from explicit instruction and writing routines that are applicable to solving these problems.

EXEMPLAR OF A WRITING THE MATH ASSIGNMENT
Student’s Name
Topic:
Date:
Class:
Part 1. The Problem
TOP Electronics is a small business with five employees. The mean (average) weekly salary for the five employees is $360. If the weekly salaries of four of the employees are $340, $340, $345, and $425, what is the salary of the fifth employee?
Part 2. What is the problem asking?
Find the salary of the fifth employee.
Part 3. Answer
The salary of the fifth employee is $350 per week.
Part 4. Explanation of Strategy
The arithmetic mean or average can be represented algebraically as:
X
 x
1
 x
2
...
n x n
I put information from the problem into the formula. The problem says there are 5 employees, so n

5 .
The problem also gives the mean (average) salary and the salaries of 4 of the employees. These numbers can be substituted into the formula as follows:
340 340 345 425

360

5
1800

340 340 345 425
 x x
5
5
 x
5
 x
5
350
 x
5
Check: 360

340 340 345 425 350

1800
5 5

360
Part 5. A New Problem
Joseph took five math exams this grading period and his average score on all of the exams is 88. He remembers that he received test scores of 78, 87, 94, and 96 on four of the examinations, but he has lost one examination and cannot remember what he scored on it. What was Joseph’s score on the missing exam?
Part 6. Answer to New Problem
Joseph received a score of 85 on the missing examination.
EVALUATION
Name and Proper Heading Part 4. Explanation of strategy. 1 Point
Part 1. Problem copied correctly?
Part 2. Understand the problem?
1/2 Point Part 5. New problem.
1/2 Point Part 6. Solution to new problem.
Part 3. Correct and complete answer? 1/2 Point
1 Point
1/2 Point
TOTAL 4 Points