please answer questions 11-13

11. Prove that for every n e Z, n2-2 is not divisible by 4. Use proof by Contradiction. Prove that if a and b are consecutive integers then the sum a + b is odd. Use proof by contrapositive. 12. 13. Let m, n 2 0 be integers. Prove that if m+n 229 then m 2 15 or n 2 15. Prove by contradiction