well..

the problem lies in trying to divise by 0. (a+b)(a-b) is 4 x 0, but b(a-b) is 2 x (2-2) and if you divide by zero, you can't. It's a Pentium III flaw and they recalled it back in 1997. (recalling arts chip please) hehe.

A for fun and games!
F for actual proof!