Please solve Questions 5-6 If you will solve only one of them I will not upvote

6, (ANSWER THIS QUESTION ON THE BACK SIDE OF THE SECOND PAPER). Let f : A B be an onto function. Define the relation R on A such that aRb if f(a)-f(b). Is R an equival ence relation? 5. Let m Z+where m is an odd integer. Prove that there exists a positive integer n such that m divides 2n-1 (Hint: You can use the pigeonhole principle.)