Question 2 a) Show by induction that n' - 3n +4 is even. [5] b) Prove that for all integer a, b and c, if a divides b and a divides c, then a divides (b+c). [5] c) If a and b are real numbers such that the product ab is an irrational number, then either a or b must be an irrational number. Prove by contraposition. [5] d) Prove by cases that if x is an integer then x' + 3x + / is odd. [5] e) Prove that 2n + 1