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Method

Graphing a Linear Inequality

Graphing a linear inequality is similar to graphing a linear equation in slope-intercept form. However, instead of a line, the graph of a linear inequality is a region of the coordinate plane. Consider the following linear inequality.
To draw its solution set, the procedure begins by writing the inequality in slope-intercept form. This way, the equation for the boundary line can be obtained. Then, this boundary line is graphed in the coordinate plane. Finally, the region that contains the solutions is shaded.
1
Write the Inequality in Slope-Intercept Form
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To find the boundary line of the region, start by writing the inequality similar to a linear equation in slope-intercept form. This is done solving the inequality for one of the variables, most commonly
Write in slope-intercept form
Then, the inequality in slope-intercept form can be written as follows.
2
Graph the Boundary Line
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The boundary line of the inequality is obtained by replacing the inequality symbol with an equals sign.
If the inequality is strict, the points on the line are not solutions to the inequality. Therefore, the line is dashed. Conversely, if the inequality is not strict, the points on the line are solutions to the inequality. In this case, the line is solid.
Symbol Meaning Type Boundary Line
Less than Strict Dashed
Greater than Strict Dashed
Less than or equal to Non-strict Solid
Greater than or equal to Non-strict Solid

Therefore, in the given example, the line is solid. The boundary line can be graphed using intercept and slope.

3
Test a Point
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The region of the coordinate plane either to the left or to the right of the boundary line contains the solution set. To determine the correct region, substitute an arbitrary test point not on the boundary line into the inequality. It is common to use
Evaluate right-hand side
Since is a true statement, the point is a solution to the inequality.
4
Shade the Correct Region
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If the test point is a solution to the inequality, the region that contains it must be shaded. Otherwise, the opposite region must be shaded.

In this case, the test point is a solution to the inequality. The region containing lies to the left of the boundary line. This is the region that must be shaded.