Linear Expressions & Single-Variable Equations/Inequalities

Lesson 5

Math

Unit 3

9th Grade

Lesson 5 of 12

Objective


Solve for a variable in an equation or formula.

Common Core Standards


Core Standards

  • A.CED.A.4 — Rearrange formulas to highlight a quantity of interest, using the same reasoning as in solving equations. For example, rearrange Ohm's law V = IR to highlight resistance R.

Foundational Standards

  • 8.EE.C.7

Criteria for Success


  1. Describe what it means when you are "solving for" a variable in an equation. 
  2. Describe how solving for a "quantity of interest" provides useful information about a relationship. 
  3. Derive multiple relationships in known formulas by solving for different variables. 

Tips for Teachers


This lesson will prepare students to fully access the standard A-CED.4, which necessitates a modeling context. This standard will be fully covered over the course of this unit.

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Anchor Problems

25-30 minutes


Problem 1

Solve the following three equations for $$x$$

$$2x+6=10$$
$$ax+6=10$$
$$ax+b=c$$

 

Guiding Questions

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Problem 2

The perimeter formula for a rectangle is $${p=2(l+w)}$$, where $$p$$ represents the perimeter, $$l$$ represents the length, and $$w$$ represents the width. 

 

Calculate $$l$$ when $$p=70$$ units and $$ w=15$$ units. 

Solve the problem in two ways: 

  1. Substitute the given values and then solve for the desired variable. 
  2. Solve for the desired variable and then substitute given values. 

Guiding Questions

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References

EngageNY Mathematics Algebra I > Module 1 > Topic C > Lesson 19Exercise 4

Algebra I > Module 1 > Topic C > Lesson 19 of the New York State Common Core Mathematics Curriculum from EngageNY and Great Minds. © 2015 Great Minds. Licensed by EngageNY of the New York State Education Department under the CC BY-NC-SA 3.0 US license. Accessed Dec. 2, 2016, 5:15 p.m..

Modified by Fishtank Learning, Inc.

Problem 3

Below is a rectangle with dimensions $$b$$ and $$h$$ and a right triangle with a height of $$h$$ and a base $$b$$. The combined area is 80 square inches.

Write an equation that solves for $$b$$ in terms of $$h$$.

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


Solve for $$x$$. Identify any domain restrictions.

$$\frac{ax+b}{c}-d=e$$

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.

Next

Write equations using defined variables to represent a contextual situation.

Lesson 6
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Lesson Map

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

Topic A: Properties and Solutions of Single-Variable Linear Expressions and Equations

Topic B: Modeling with Single-Variable Linear Equations

Topic C: Properties and Solutions of Single-Variable Linear Inequalities

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