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You are reading an older version of this FlexBook® textbook: CK-12 Algebra I Concepts - Honors Go to the latest version.

2.15: Graphical Solutions to Absolute Value Inequalities

Difficulty Level: Advanced Created by: CK-12
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Practice Graphs of Absolute Value Inequalities
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Solve the following inequality and graph the solution on a number line.

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Khan Academy Absolute Value Inequalities on a Number Line

Guidance

Recall that you can graph linear inequalities on number lines. For , the graph can be shown as:

Notice that there is only one solution set and therefore one section of the number line has the region shown in red.

What do you think would happen with absolute value linear inequalities? With absolute value linear inequalities, there are two inequalities to solve. Therefore there can be two sections of the number line showing solutions.

For , you would actually solve for and . If you were to graph this solution on a number line it would look like the following:

The solution is OR .

For , you would actually solve for and . If you were to graph this solution on a number line it would look like the following:

The solution is . This is the same as AND .

Graphing the solution set to an absolute value linear inequality gives you the same visual representation as you had when graphing the solution set to linear inequalities. The same rules apply when graphing absolute values of linear inequalities on a real number line. Once the solution is found, the open circle is used for absolute value inequalities containing the symbols > and <. The closed circle is used for absolute value inequalities containing the symbols and .

Example A

Represent the solution set to the following inequality on a number line: .

Solution: First solve the inequality. Then, represent your solution on a number line.

The solution sets are OR .

Example B

Solve the following inequality and graph the solution on a number line:

Solution: First solve the inequality. Then, represent your solution on a number line.

The solution sets are , OR .

Example C

Solve the following inequality and graph the solution on a number line:

Solution: First solve the inequality. Then, represent your solution on a number line.

The solution is .

Concept Problem Revisited

Solve the following inequality and graph the solution on a number line.

First solve the inequality:

The solution is .

Representing on a number line:

Vocabulary

Absolute Value Linear Inequality
Absolute Value Linear inequalities can have one of four forms: , or . Absolute value linear inequalities have two related inequalities. For example for , the two related inequalities are and .
Number Line
A number line is a line that matches a set of points and a set of numbers one to one.

Guided Practice

1. Represent the solution set to the inequality on a number line.

2. Represent the solution set to the inequality on a number line.

3. Represent the solution set to the inequality on a number line.

Answers:

1.

The solution sets are or .

2.

The solution sets are or .

3.

The solution sets are or .

Practice

Represent the solution sets to each absolute value inequality on a number line.

Vocabulary

Absolute Value Linear inequalities

Absolute Value Linear inequalities

Absolute value linear inequalities can have one of four forms |ax + b| > c, |ax + b| < c, |ax + b| \ge c, or |ax + b| \le c. Absolute value linear inequalities have two related inequalities. For example for |ax+b|>c, the two related inequalities are ax + b > c and ax + b < -c.
number line

number line

A number line is a line on which numbers are marked at intervals. Number lines are often used in mathematics to show mathematical computations.

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Difficulty Level:

Advanced

Grades:

Date Created:

Apr 30, 2013

Last Modified:

Sep 21, 2015
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