Let i be the complex number (0,1)

Show that i = (0,1) and (0, -1) are the only square roots of -1. Hint: Suppose that (x,y)(x,y) = (-1,0) and show that x = 0 and y = +-1. You can use the fact that, for real numbers, the only square roots of positive 1 are +-1. You also know that x^2 >= 0.

I have no idea what to do...Any advice?