17. In each of the following, two open sentences P(x, y) and Q(x,y) are given, where the domain of both x and y is Z. Determine the truth value of P(x,y) Q(x, y) for the given values of x and y. (a) P(x, y): x2 - y2 = 0. and Q(x, y): x = y. (x, y) {(1, -1), (3, 4), (5,5)}. (b) P(x, y): (x = lyl. and Q(x, y): x = y. (x, y) {(1,2), (2,-2), (6, 6)). (c) P(x, y): x2 + y2 = 1. and Q(x, y): x+y=1. (x, y) {(1, -1), (-3,4), (0, -1), (1, 0)}