There is an old saying which goes, you can never prove a negative. In other words you can only prove what will happen not what won't happen. In number theory, Fermat's Last Theorem states that no three positive integers a, b, and c can satisfy the equation a^n + b^n = c^n for any integer value of n greater than two. So how do you go about proving this? Andrew Wiles did it in 1994 but how did he prove a negative?