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Linear Inequalities and Systems of Linear Inequalities in Two Variables
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Graphical Method of Solving Systems of Linear Inequalities in Two Variables

To solve a system of linear inequalities graphically, graph each inequality of the system on the same set of axes, and then determine the region where their graphs overlap. Such region represents the solution set of the system.

Example 1

Graph the solution set of the following system of linear inequalities:

{   x+y > 5 x+y3


Solution

First, graph each linear inequality of the given system. The graph of x+y > 5 has a dashed boundary line with the equation x+y=5.

Using (0,0) as the test point, you will get 0 > 5, which is false. Hence, the graph of x+y > 5 is the region on the side of the boundary line not containing the point (0,0). Refer to the following figure:

For x+y3, the boundary line is a solid line with the equation x+y=3. Using (0,0) again as the test point, you will obtain 03, which is false. Thus, the graph of x+y3 is the region that does not contain the point (0,0) and includes the boundary line, as shown in the following figure:

Combine the two preceding graphs on the same set of axes and shade the region where they overlap. The resulting region (which is shown in the figure below) is the solution set of the given system of linear inequalities.