Let C=(3,5) be the midpoint of AB, where A=(1,-8) and B = (x,y). What is the value of xy?
Using the midpoint rule :
(x + 1) / 2 = 3 (y - 8) / 2 = 5
x + 1 = 6 y - 8 = 10
x = 6 - 1 = 5 y = 10 + 8 = 18
xy = 5*18 = 90
