6. using proof by contrapositive, prove the following: let n e z2°. if n mod 4 e {2,3}, then n is not a perfect square note: for integers k > 0 and n, the integer n is divided by k. for example, 7 mod 3 is 1. if you are not familiar with called modulus) take a there exists some non-negative integer m such that m2 = n n mod k is defined as the remainder when mod (also quick read through chapter 2.2. an integer n is a perfect square if