Answer: Bottom left corner
Let n be an odd number. Because 4n is a multiple of 2, it is an even number.
============================================
Explanation:
The square has a side length of n, so its perimeter is 4n since n+n+n+n = 4n.
We can rewrite 4n as 2*2n = 2m where m = 2n is an integer. Any number in the form 2*(some integer) is always even. Even numbers always have 2 as a factor.
So whenever it comes to proving something is even, the ultimate goal is to get it into the form 2*(some integer). If we can do this, then the number is even. If not, then the number is odd.