Quadratic Functions and Solutions

Lesson 5

Math

Unit 7

9th Grade

Lesson 5 of 13

Objective


 Identify solutions to quadratic equations using the zero product property (equations written in intercept form).

Common Core Standards


Core Standards

  • A.APR.B.3 — Identify zeros of polynomials when suitable factorizations are available, and use the zeros to construct a rough graph of the function defined by the polynomial.
  • F.IF.C.8.A — Use the process of factoring and completing the square in a quadratic function to show zeros, extreme values, and symmetry of the graph, and interpret these in terms of a context.

Criteria for Success


  1. Describe the zero product property: in order for a product to be zero, at least one of the factors must be zero. 
  2. Understand the solutions to a quadratic equation as the roots of the function or the $$x$$-intercepts of the graph.
  3. Use the zero product property to determine the solutions of a quadratic equation when written in intercept form.

Tips for Teachers


  • This lesson focuses on students’ understanding of finding the solutions to a quadratic function when it is written in intercept form. In the upcoming lessons, students will learn how to factor trinomials into this form; this lesson demonstrates to students the value of having a function written in this form to find the solutions. 
  • If Factoring Trinomials Is Aspirin, Then How Do You Create The Headache? by Dan Meyer is a worthwhile read on why factoring is valuable.
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Anchor Problems


Problem 1

Consider the equation $${a\times b=0}$$. What can you conclude about the values of $$a$$ and $$b$$?

Consider the equation $$(a+2)(b-1)=0$$. What can you conclude about the values of $$a$$ and $$b$$?

Guiding Questions

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Problem 2

The solutions to a quadratic equation are given by the $${x-}$$intercepts of the graph. What are the solutions to the quadratic equation graphed below?

The equation for the parabola shown is $$y=({x-}3)(x+2)$$. Show algebraically that the solutions to the quadratic equation are the same as those seen in the graph.

Guiding Questions

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Problem 3

A quadratic function is shown in the graph below. 

The equation for this function is $${y=(x+a)(2x+b)}$$. What are possible values for $$a$$ and $$b$$?

Guiding Questions

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Problem Set


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

Target Task


Problem 1

For each equation below, use the zero product property to find all solutions. Explain each step in your reasoning.

a.  $${x(13-4x)=0}$$

b.  $${7(y+12)=0}$$

c.  $${(x-19)(x+3)=0}$$

d.  $${(y-6)(3z-4)=0}$$

References

Illustrative Mathematics Zero Product Property 3

Zero Product Property 3, accessed on July 2, 2018, 10:37 a.m., is licensed by Illustrative Mathematics under either the CC BY 4.0 or CC BY-NC-SA 4.0. For further information, contact Illustrative Mathematics.

Modified by Fishtank Learning, Inc.

Problem 2

Which equation represents the graph shown below? Explain your reasoning.

a.  $${y=(x-3)(x+6)}$$

b.  $${y=(x+3)(x-6)}$$

c.  $${y=(x-3)(x-6)}$$

d.  $${y=(x+3)(x+6)}$$

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.

  • Give students equations in intercept form and have them determine the solutions and sketch a possible graph of the function
  • Give students graphs of parabolas with the $${x-}$$intercepts shown and have them determine the solutions and write a possible equation for the function
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Lesson 4

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Lesson 6

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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