Let's now use the point (0,0), which is on the boundary line, to determine the region we should shade. If substituting the point in the inequality produces a true statement, then the region to be shaded is the one which contains the point. Otherwise, we should shade the opposite region.
The test point produced a true statement. We should shade the half-plane that contains this point. But... what is this region?
We are not able to determine the region, because the test point lies on the boundary line. Choosing a test point on the boundary line does not help us to determine the half-plane we should shade.
Let's test the point (- 2,2), which is not on the boundary line.
We obtained a true statement, and we should shade the region that contains the point. This time, it should not be hard to identify the half-plane, since (- 2,2) is not on the boundary line.
