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# ZingPath: Solving Linear Inequalities

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## Solving Linear Inequalities

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### Lesson Focus

#### Graphing Linear Inequalities in Two Variables

Pre-Algebra

Students graph linear inequalities in two variables on the coordinate plane.

### Now You Know

After completing this tutorial, you will be able to complete the following:

• Graph a linear inequality in two variables using a test point.
• Graph a linear inequality in two variables without using a test point.

### Everything You'll Have Covered

Graphing linear equations into variables compared to linear inequalities in two variables

You are probably familiar with graphing a linear equation in two variables. A linear equation is graphed by plotting two or more points on a coordinate plane that make the equation true. If the points satisfy the equation, they follow a straight line.

Consider the linear equation y = 2x + 2, shown on the right.

The ordered pairs graphed on the coordinate plane are:

(-3, -4), (-2, -2), (0, 2), (1, 4), (-4, -6)

All the numbers on the line satisfy the linear equation y = 2x + 2.

Graphing linear inequalities is similar to graphing linear equations, except that the line (called the boundary line for inequalities) may or may not be included in the solution set. Plus, a half-plane is included.

The linear equation is changed to an inequality by changing the equal sign to , resulting in the inequality y 2x + 2.

The related boundary line is y = 2x + 2. We know the graph of this line. To find which half-plane to shade, identify a test point. (0, 0) is a good point to use, since the calculation will be easier. Substituting the values in the inequality, we find that:

The test point makes the linear inequality false. So, the half-plane that does not include the test point is shaded. If the test point had made the inequality true, the other half-plane would be in the solution set.

Steps to graph a linear equation

• Identify the boundary line by graphing two ordered pairs.
• If there is a ? or ? inequality, we use a solid line to graph the boundary line. If there is a < or > inequality, we use a dashed line to graph the boundary line.
• Choose a test point to determine which half-plane is part of the solution set for the inequality. If the test point is part of the solution set, that half-plane satisfies the inequality. If the test point is not part of the solution set, the other half-plane satisfies the inequality.
• Shade the half-plane which satisfies the inequality.

Graphing a linear inequality without using a test point

You can determine the half-plane that satisfies the linear inequality without using a test point. Isolate y and then apply the following rules to shade the half-plane.

### Tutorial Details

 Approximate Time 40 Minutes Pre-requisite Concepts Students should be familiar with these concepts: coordinate plane, definition of an inequality and a linear inequality in two variables, how to graph a linear equation in two variables, and solving linear equations in two variables. Course Pre-Algebra Type of Tutorial Skills Application Key Vocabulary boundary line, coordinate plane, graphing