It's almost the same thing as variance of a sample. You just divide by n instead of n minus 1. Variance of a population is equal to, when you take each of the data points, x sub i, you subtract from that the mean, you square it, and then you take the average of all of these. So you add the squared distance for each of these points from i equals 1 to i is equal to n, and you divide it by n. So let's see what happens if we can, I don't know, maybe we want to multiply out the squared term and see where it takes us. So let's see. And I think it'll take us someplace interesting. So this is the same thing as the sum from i is equal to 1 to n. Let's see, this we just multiply it out.