Proof by contradiction was my favorite method in college.  I think it's easier because you know where to start and you just move forward.  So even to prove that things are true, I'd just assume the converse and show a contradiction.

Because a non-contradiction based proof seems harder.  You know where you want to go, but you don't know where to start.

Scroogey

Pulling out an inductive proof by contradiction, along with an obscure (to me) formula, is impressive for someone who doesn't do proofs on a regular basis :)
