Proof: Let's assume that F is an ordered field and a is an element of F. We want to prove that a^2 is greater than or equal to 0.
To begin, we know that in an ordered field, the product of two positive numbers is also positive. Therefore, a * a is positive since a is not equal to 0 (as 0 * 0 = 0).
Now, let's consider the case where a is negative. In an ordered field, the product of a negative number and a positive number is negative. Since a is negative and a is not equal to 0, a * a is negative.
Lastly, if a is equal to 0, then a * a is equal to 0 as well.
In all cases, a * a is either positive or equal to 0. Therefore, we can conclude that a^2 is greater than or equal to 0 for every a in F.