3. (a) Prove VnN+,aEN+,bEN+,abSn)agxorng. (b) Prove Vac E N+,:L' composite > 3p 6 N+,p is prime and p g and p | x. (c) One way to test whether a number is prime is the following: Given an integer n > 1, check if n is divisible by any prime number less than equal to its square root. If n is not divisible by any of these primes, then n prime. Write the contrapositive of 3b). Your solution should be written so that it clearly shows that the above test is indeed a valid method