Example

Solving {4x+3y12,  y<43x+1}\{4x + 3y \geq 12,\; y < -\frac{4}{3}x + 1\} by Graphing

Solve the system {4x+3y12y<43x+1\left\{\begin{array}{l} 4x + 3y \geq 12 \\ y < -\frac{4}{3}x + 1 \end{array}\right. by graphing.

Graph 4x+3y124x + 3y \geq 12. The boundary line is 4x+3y=124x + 3y = 12, which has intercepts x=3x = 3 and y=4y = 4. Because the inequality uses \geq (non-strict), draw a solid line. Test (0,0)(0, 0): 4(0)+3(0)=0124(0) + 3(0) = 0 \geq 12 is false. So shade the side that does not contain (0,0)(0, 0).

Graph y<43x+1y < -\frac{4}{3}x + 1 on the same grid. The boundary line is y=43x+1y = -\frac{4}{3}x + 1, which has slope m=43m = -\frac{4}{3} and y-intercept b=1b = 1. Because the inequality uses << (strict), draw a dashed line. Test (0,0)(0, 0): 0<43(0)+10 < -\frac{4}{3}(0) + 1 gives 0<10 < 1, which is true. So shade the side that contains (0,0)(0, 0).

Identify the solution. The two boundary lines are parallel — both have slope 43-\frac{4}{3} — and the shaded regions face away from each other. Because there is no point that lies in both shaded regions at the same time, the system has no solution.

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Updated 2026-04-21

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