SOLUTION: Write an indirect proof. If n/2 is an integer, then n is even.

You can put this solution on YOUR website!
Lemma: if n/2 is an integer, n is an integer.
Proof: Unproved, pretty intuitive.
Theorem: if n/2 is an integer, n is even.
Proof: Suppose n isn't even. Then n is odd, as n is an integer, and all integers are dichotomous (even or odd). Then n=2k+1, where k is an integer. (2k+1)/2 = k+1/2. This isn't an integer. -><-, contradiction. Therefore, n is even.