12) [1 points] To prove that if 4x2 is even, then x is even, we use a) The direct proof b) The vacuous proof c) The trivial proof d) The contrapositive proof e) The statement is invalid. 13) [1 points] To prove the proposition P(1), where P(n) is the proposition "If n is a positive integer, then n2n." What kind of proof did you use? a) The direct proof b) The vacuous proof c) The trivial proof d) The contrapositive proof e) The statement is invalid