According to trinitarians is 0.999... = 1 = 3 
But seriously, there are many different proofs you can do to prove 0.999...=1, its in the thread fr0d0 linked. Don't raise this monster again, necromancer.

But seriously, there are many different proofs you can do to prove 0.999...=1, its in the thread fr0d0 linked. Don't raise this monster again, necromancer.