Which relation is a function? a) x y = y2 - 3 b) y x = y2 - 3 c) x2 + y2 = 5 + x d) x2 - y = 10x + 25 + y

Since you didn’t specify that it needed to be y as a function of x, all of the above equalities can be rewritten as functions. However, in case that you meant to imply that, A and B are both not valid for y as a simple function of x.