Explain why you can use a test point to determine which region or regions of the graph of an inequality should be shaded.

A curve divides a plane into two areas, one satisfying the inequality (shaded) and one that does not (unshaded). So we can pick a point on either side (not on the curve itself) and substitute its x- and y-coordinates into the inequality. If the substituted values make the inequality true, then that point is in the shaded area. Otherwise, that point is in the unshaded area.