Use proof by contradiction to show the claim. (a) Let a > 0 be an irrational number. Then a is irrational as well. (b) Let n be a natural number>2. Then (n^2 - n + 1)/(n + 1) is not an integer. [Hint: Write n^2 - n + 1 = (n + 1)(n 2) + 3.] (C) PA ((~Q) (~P))) Q is a tautology