That's how we can denote it just like that. That is the mean of the y squared. Or if you multiply both sides of this equation by n, you get y1 squared plus y2 squared plus all the way to, all the way to yn squared, yn squared is equal to n, is equal to n, let me do this in different colors, is equal to, so this is, this is equal to n, this n times the mean of the squared values of y. And notice, this is exactly, this is exactly what we have over here. That is n times the mean of the squared values of y or the mean of the y squareds. That's exactly what that is and we can do that with each of these terms. What is, what is x1, x1, y1 plus x2, y2 plus all the way to, all the way to xn, yn.