I'm having quite a bit of trouble with proofs.

(1) Prove using the contrapositive approach: Ifxis positive then so isx +1.

(2) Let x and y be positive integers. Prove thatx<yif and only ifx^2 <y^2.

(3) Prove using cases that the sum of 3 consecutive integers is divisible by 3.

I just don't get proofs.