So let's see, what is mu equal to? What is the mean? The mean is just equal to the sum from i is equal to 1 to n of each of the terms. You just take the sum of each of the terms, and you divide by the number of terms there are. So that is equal to, so if we look at this thing, this thing can be written as, let me draw a line here, this thing can be written as the sum from i is equal to 1 to n of xi squared, all of that over n, minus mu squared. Well, mu is this. So this thing squared.