altivo

This thing popped up as a fortune cookie on Linux this morning. It took me a while to figure out where the error was. Let's see who can find it first.

Proof that 2 equals 1:

x = y	[Given]
x² = xy	[Multiply both sides by x]
x² - y² = xy - y²	[Subtract y² from both sides]
(x + y)(x - y) = y(x - y)	[Factor]
(x + y) = y	[Cancel out (x - y) term]
2y = y	[Substitute x for y, by original equation]
2 = 1	[Divide both sides by y]

I'll supply the answer after folks take a crack at it. It isn't as hard as it looks, and someone may get it right away, so ~~replies are screened for now~~. It was credited to Omni Magazine.

Answer:
I declare

quaxo the first to put his paw right on the heart of the error, though you were all on the right track. If X = Y, then (X - Y) = 0. And the fourth step ("Cancel out (X - Y) term") is actually a divide by zero error. Up to that point, everything was perfectly kosher, even though some of it was nonsensical. After that, nothing is right.