Proof techniques 1. Prove that the product of two odd numbers is odd. 2. Prove that if n is perfect square, then n+2 is not a perfect square¹ 3. Prove that if n is an integer and 3n+2 is even, then n is even using (a) a proof by contraposition. (b) a proof by contradiction. 4. Prove that if n is a positive integer, then n is even if and only if 7n +4 is even.