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Graph the linear inequality y < 5 .

The graph shows the x y-coordinate plane. The x- and y-axes each run from negative 10 to 10. The line y equals 5 is plotted as a dashed arrow horizontally across the plane. The region above the line is shaded.

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Graph the linear inequality y −1 .

The graph shows the x y-coordinate plane. The x- and y-axes each run from negative 10 to 10. The line y equals negative 1 is plotted as a dashed arrow horizontally across the plane. The region below the line is shaded.

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Key concepts

  • To Graph a Linear Inequality
    1. Identify and graph the boundary line.
      If the inequality is or , the boundary line is solid.
      If the inequality is<or>, the boundary line is dashed.
    2. Test a point that is not on the boundary line. Is it a solution of the inequality?
    3. Shade in one side of the boundary line.
      If the test point is a solution, shade in the side that includes the point.
      If the test point is not a solution, shade in the opposite side.

Practice makes perfect

Verify Solutions to an Inequality in Two Variables

In the following exercises, determine whether each ordered pair is a solution to the given inequality.

Determine whether each ordered pair is a solution to the inequality y > x 1 :

( 0 , 1 )
( −4 , −1 )
( 4 , 2 )
( 3 , 0 )
( −2 , −3 )

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Determine whether each ordered pair is a solution to the inequality y > x 3 :

( 0 , 0 )
( 2 , 1 )
( −1 , −5 )
( −6 , −3 )
( 1 , 0 )

yes  no  no  yes  no

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Determine whether each ordered pair is a solution to the inequality y < x + 2 :

( 0 , 3 )
( −3 , −2 )
( −2 , 0 )
( 0 , 0 )
( −1 , 4 )

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Determine whether each ordered pair is a solution to the inequality y < x + 5 :

( −3 , 0 )
( 1 , 6 )
( −6 , −2 )
( 0 , 1 )
( 5 , −4 )

yes  no  no  yes  yes

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Determine whether each ordered pair is a solution to the inequality x + y > 4 :

( 5 , 1 )
( −2 , 6 )
( 3 , 2 )
( 10 , −5 )
( 0 , 0 )

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Determine whether each ordered pair is a solution to the inequality x + y > 2 :

( 1 , 1 )
( 4 , −3 )
( 0 , 0 )
( −8 , 12 )
( 3 , 0 )

no  no  no  yes  yes

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Recognize the Relation Between the Solutions of an Inequality and its Graph

In the following exercises, write the inequality shown by the shaded region.

Write the inequality shown by the graph with the boundary line y = 3 x 4 .

The graph shows the x y-coordinate plane. The x- and y-axes each run from negative 10 to 10. The line y equals 3x minus 4 is plotted as a dashed line extending from the bottom left toward the top right. The region to the right of the line is shaded.
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Write the inequality shown by the graph with the boundary line y = 2 x 4 .

The graph shows the x y-coordinate plane. The x- and y-axes each run from negative 10 to 10. The line y equals 2x minus 4 is plotted as a solid line extending from the bottom left toward the top right. The region below the line is shaded.

y < 2 x 4

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Write the inequality shown by the graph with the boundary line y = 1 2 x + 1 .

The graph shows the x y-coordinate plane. The x- and y-axes each run from negative 10 to 10. The line y equals negative one-half x plus 1 is plotted as a solid line extending from the bottom left toward the top right. The region below the line is shaded.
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Write the inequality shown by the graph with the boundary line y = 1 3 x 2 .

The graph shows the x y-coordinate plane. The x- and y-axes each run from negative 10 to 10. The line y equals negative one-third x minus 2 is plotted as a solid line extending from the top left toward the bottom right. The region below the line is shaded.

y 1 3 x 2

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Write the inequality shown by the shaded region in the graph with the boundary line x + y = 5 .

The graph shows the x y-coordinate plane. The x- and y-axes each run from negative 10 to 10. The line x plus y equals 5 is plotted as a solid line extending from the top left toward the bottom right. The region above the line is shaded.
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Write the inequality shown by the shaded region in the graph with the boundary line x + y = 3 .

The graph shows the x y-coordinate plane. The x- and y-axes each run from negative 10 to 10. The line x plus y equals 3 is plotted as a solid line extending from the top left toward the bottom right. The region above the line is shaded.

x + y 3

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Write the inequality shown by the shaded region in the graph with the boundary line 2 x + y = −4 .

The graph shows the x y-coordinate plane. The x- and y-axes each run from negative 10 to 10. The line 2 x plus y equals negative 4 is plotted as a solid line extending from the top left toward the bottom right. The region below the line is shaded.
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Write the inequality shown by the shaded region in the graph with the boundary line x + 2 y = −2 .

The graph shows the x y-coordinate plane. The x- and y-axes each run from negative 10 to 10. The line x plus 2 y equals negative 2 is plotted as a solid line extending from the top left toward the bottom right. The region below the line is shaded.

x + 2 y −2

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Write the inequality shown by the shaded region in the graph with the boundary line 3 x y = 6 .

The graph shows the x y-coordinate plane. The x- and y-axes each run from negative 10 to 10. The line 3 x minus y equals 6 is plotted as a dashed line extending from the bottom left toward the top right. The region to the left of the line is shaded.
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Write the inequality shown by the shaded region in the graph with the boundary line 2 x y = 4 .

The graph shows the x y-coordinate plane. The x- and y-axes each run from negative 10 to 10. The line 2 x minus y equals 4 is plotted as a dashed line extending from the bottom left toward the top right. The region to the left of the line is shaded.

2 x y < 4

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Write the inequality shown by the shaded region in the graph with the boundary line 2 x 5 y = 10 .

The graph shows the x y-coordinate plane. The x- and y-axes each run from negative 10 to 10. The line 2 x minus 5 y equals 10 is plotted as a dashed line extending from the bottom left toward the top right. The region below the line is shaded.
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Write the inequality shown by the shaded region in the graph with the boundary line 4 x 3 y = 12 .

The graph shows the x y-coordinate plane. The x- and y-axes each run from negative 10 to 10. The line 4 x minus 3 y equals 12 is plotted as a dashed line extending from the bottom left toward the top right. The region below the line is shaded.

4 x 3 y > 12

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Graph Linear Inequalities

In the following exercises, graph each linear inequality.

Graph the linear inequality y > 2 3 x 1 .

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Graph the linear inequality y < 3 5 x + 2 .

The graph shows the x y-coordinate plane. The x- and y-axes each run from negative 10 to 10. The line y equals three-fifths x plus 2 is plotted as a dashed line extending from the bottom left toward the top right. The region below the line is shaded.

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Graph the linear inequality y 1 2 x + 4 .

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Graph the linear inequality y 1 3 x 2 .

The graph shows the x y-coordinate plane. The x- and y-axes each run from negative 10 to 10. The line y equals negative one-third x minus 2 is plotted as a solid line extending from the top left toward the bottom right. The region below the line is shaded.

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Graph the linear inequality x y 3 .

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Graph the linear inequality x y −2 .

The graph shows the x y-coordinate plane. The x- and y-axes each run from negative 10 to 10. The line x minus y equals negative 2 is plotted as a solid line extending from the bottom left toward the top right. The region below the line is shaded.

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Graph the linear inequality 4 x + y > −4 .

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Graph the linear inequality x + 5 y < −5 .

The graph shows the x y-coordinate plane. The x- and y-axes each run from negative 10 to 10. The line x plus 5 y equals negative 5 is plotted as a dashed line extending from the top left toward the bottom right. The region below the line is shaded.

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Graph the linear inequality 3 x + 2 y −6 .

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Graph the linear inequality 4 x + 2 y −8 .

The graph shows the x y-coordinate plane. The x- and y-axes each run from negative 10 to 10. The line 4 x plus 2 y equals negative 8 is plotted as a solid line extending from the top left toward the bottom right. The region to the right of the line is shaded.

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Practice Key Terms 3

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Source:  OpenStax, Elementary algebra. OpenStax CNX. Jan 18, 2017 Download for free at http://cnx.org/content/col12116/1.2
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