3 = 1

There are various ways to prove that 3 = 1.
(The fun is in finding the catch, but let us just "prove" it first)

Let x = y
Then x^2 = xy
or 3x^2 = x^2 + 2xy
We may also write 3x^2 - 3xy = x^2 - xy
i.e. 3(x^2 - xy) = 1(x^2 - xy)
or 3 = 1 (x^2 - xy) / (x^2 - xy)
i.e. 3 = 1