(2 points) let u = {1,2,3,4,5,6}. determine x({2,3,5}) even integer and an odd integer is odd 12. (10 points) give a direct proof that the sum of an 13. (10 points) give an indirect proof that if n3 is even, then n is even. 14. (10 points) give a proof by contradiction that if 3n 2 is odd, then n is odd m |n] m and n, we have mn 15. (10 points) give a proof by cases that for any integers