I'm having quite a bit of trouble with proofs.
(1) Prove using the contrapositive approach: If x is positive then so is x + 1.
(2) Let x and y be positive integers. Prove that x<y if and only if x^2 < y^2.
(3) Prove using cases that the sum of 3 consecutive integers is divisible by 3.
I just don't get proofs.