Help with these 4 questions please

Question 4 1 pts Definition: A real valued function f(a) is called one-to-one if for all 31 and 32 real numbers, if x1 2, then f(x)f(x2) Suppose you are trying to prove that f(x)31 is one-to-one by using contrapositive proof. Which of the following should be the first sentence of your proof? Assume x1T2. Assume f (x) /(r2) for some ri , r2 Assume x1 = .r2. c) Assume f (n )f (z2 ) for some Question 5 1 pts Suppose you are trying to prove that f(x) = x3 is one-to-one by using contrapositive proof: Which of the following should be the last sentence of your proof? () Therefore f (x 1) f(r2) for some r 1T2. Therefore f (x) = f(x2) for some ri . 22. Therefore x1 O Therefore rl =2"2. Question6 1 pts Suppose you are trying to prove the following Proposition: Proposition 2: If a is an odd integer, then a2 +3a + 5 is odd. Which method would you choose? Contrapositive Proof. Direct Proof DQuestion 7 1 pts Suppose you are trying to prove the following Proposition: Proposition 3 Suppose r. y Z. If a2( +3) is even, then z is even or y is odd. Which method would you choose? Direct Proof Contrapositive Proof