Quadratic Functions and Solutions

Lesson 3

Math

Unit 7

9th Grade

Lesson 3 of 13

Objective


Calculate and compare the average rate of change for linear, exponential, and quadratic functions.

Common Core Standards


Core Standards

  • F.IF.B.4 — For a function that models a relationship between two quantities, interpret key features of graphs and tables in terms of the quantities, and sketch graphs showing key features given a verbal description of the relationship. Key features include: intercepts; intervals where the function is increasing, decreasing, positive, or negative; relative maximums and minimums; symmetries; end behavior; and periodicity. Modeling is best interpreted not as a collection of isolated topics but in relation to other standards. Making mathematical models is a Standard for Mathematical Practice, and specific modeling standards appear throughout the high school standards indicated by a star symbol (★). The star symbol sometimes appears on the heading for a group of standards; in that case, it should be understood to apply to all standards in that group.
  • F.IF.B.6 — Calculate and interpret the average rate of change of a function (presented symbolically or as a table) over a specified interval. Estimate the rate of change from a graph. Modeling is best interpreted not as a collection of isolated topics but in relation to other standards. Making mathematical models is a Standard for Mathematical Practice, and specific modeling standards appear throughout the high school standards indicated by a star symbol (★). The star symbol sometimes appears on the heading for a group of standards; in that case, it should be understood to apply to all standards in that group.
  • F.LE.A.3 — Observe using graphs and tables that a quantity increasing exponentially eventually exceeds a quantity increasing linearly, quadratically, or (more generally) as a polynomial function.

Foundational Standards

  • F.IF.A.2

Criteria for Success


  1. Compare the average rate of change between a linear function, exponential function, and quadratic function over specific intervals. 
  2. Describe intervals of a quadratic function where the average rate of change is increasing, decreasing, or zero. 
  3. Understand that the average rate of change of a quadratic function will eventually exceed that of a linear function but will not eventually exceed that of an exponential function. 
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Anchor Problems

25-30 minutes


Problem 1

Three functions and their graphs are shown below.

  1. Determine the average rate of change of each function over the intervals:
    1.  $${1≤x≤2}$$
    2.  $${1≤x≤3}$$
    3.  $${1≤x≤10}$$
  2. Over the interval $${1≤x≤10}0$$, order the functions from the smallest rate of change to the greatest rate of change. Can you order the functions without performing calculations? Explain your reasoning. 

Guiding Questions

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Problem 2

Below is the graph of function $${{{{f(x)}}}=(x-2)^2-4}$$.

  1. Name an interval where $${{{f(x)}}}$$ has a decreasing average rate of change. Show this algebraically. 
  2. Name an interval where $${{{f(x)}}}$$ has an increasing average rate of change. Show this algebraically. 
  3. Name an interval where $${{{f(x)}}}$$ has a zero average rate of change. Show this algebraically. 

Guiding Questions

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Problem Set

15-20 minutes


Give your students more opportunities to practice the skills in this lesson with a downloadable problem set aligned to the daily objective.

Target Task

5-10 minutes


A linear function, $${j(x)}$$, and a quadratic function, $${h(x)}$$, are shown in the graph below. 

  1. Find the average rate of change of each function over the interval $${ 1≤x≤6}$$. Which function has the greater average rate of change? 
  2. Over which interval is the average rate of change exactly the same for both the linear function and the quadratic function? 
  3. As $$x$$ increases, which function will have the greater average rate of change? Explain your reasoning. 

Additional Practice


The following resources include problems and activities aligned to the objective of the lesson that can be used for additional practice or to create your own problem set.

  • Find and compare average rates of change of different functions (linear, exponential, quadratic) over different intervals from tables, graphs, and equations
  • Inside Mathematics Performance Assessment Tasks Grades 3-High School Functions(Students do not need to write the equation for the quadratic function from the graph)
  • Mathematics Vision Project: Secondary Mathematics Two Module 1: Quadratic FunctionsLesson 1.4 "Go" and Lesson 1.5 "The Tortoise and the Hare" and "Set"

Next

Factor quadratic expressions using the greatest common factor. Demonstrate equivalence between expressions by multiplying polynomials.

Lesson 4
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Lesson Map

A7CB09C2-D12F-4F55-80DB-37298FF0A765

Topic A: Features of Quadratic Functions

Topic B: Factoring and Solutions of Quadratic Equations

Topic C: Interpreting Solutions of Quadratic Functions in Context

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