Example

Writing the Inequality x4y8x - 4y \leq 8 from Its Graph

To determine the inequality represented by a graph when its boundary line is known, such as x4y=8x - 4y = 8, observe the line style and test a point in the shaded region. If the boundary line is graphed as a solid line, points on the line are included in the solution set, meaning the inequality must use either \leq or \geq. To decide which symbol to use, select a test point from the shaded solution region. If the top-left half is shaded and contains the origin (0,0)(0, 0), substitute x=0x = 0 and y=0y = 0 into the expression x4yx - 4y: 04(0)=00 - 4(0) = 0. Since the chosen test point must produce a true statement, compare 00 to the right-side value 88. Because 0<80 < 8 is a true statement, the shaded region corresponds to the 'less than' case. Combining this with the solid line observation yields the final inequality: x4y8x - 4y \leq 8.

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Updated 2026-04-23

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Ch.3 Graphs and Functions - Intermediate Algebra @ OpenStax

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