Exercise 43 Page 254

The most common point to use as a test point is (0,0). However, this point cannot be used as a test point when it is on the boundary line. For example, let's look at the graph of y

If the point (0,0) is part of the line, it will never satisfy a strict inequality and will always satisfy a non-strict inequality. In this case, another point that is not on the line will need to be used. There are an infinite number of other points to choose, as long as they are not found on the boundary line.