The square of a number is always nonnegative.

The square of a number is always nonnegative.

This is true, and here is why:

Suppose you have a positive number n.
n^2 = n * n
A positive times a positive is a positive

Suppose you have a negative number -n
(-n)^2 = -n * -n = n^2
A negative times a negative is a positive.