The answer is 12.5 First use the distance formula to calculate the length of the 3 sides. You will get the ratios of the sides to be 1:1: root 2. This is a 45-45-90 triangle. The distance between PQ = Sq rt of (4-0)^2 + (0-3)^2 = 5. Similarly distance PR = 5 and distance QR =root 50 = 5rt2 Therefor...