Write an absolute value inequality for the following: Do not solve.

A solid at 50°C will change to a gas or liquid if the temperature t increases or decreases more than 50°C.

Here are the coordinates for eight points on the coordinate plane (q > p > 0): a (0, 0), b (p, 0), c (q, 0), d (p + q, 0), e (0, q), f (p, q), g (q, q), and h (p + q, q). which four points, if any, are on the vertices of a square?