OK, so have you ever come across this?
1=2: A Proof using Beginning Algebra
The Fallacious Proof:
* Step 1: Let a=b.
* Step 2: Then a^2 = ab,
* Step 3: a^2 + a^2 = a^2 + ab,
* Step 4: 2 a^2 = a^2 + ab,
* Step 5: 2 a^2 - 2 ab = a^2 + ab - 2 ab,
* Step 6: and 2 a^2 - 2 ab = a^2 - ab.
* Step 7: This can be written as 2 (a^2 - a b) = 1 (a^2 - a b),
* Step 8: and cancelling the (a^2 - ab) from both sides gives 1=2.
OK, OK, maybe you haven't but for geeks this is actually pretty funny. You know the conclusion is false, but it's hard to figure out where the error is. So you work on it a while, then you Google it, then you give it to a gullible friend to convince him 1 actually does equal 2, just so you can mock him for not knowing better when he believes you.