Then you have minus 2m times all of these terms. So you have, actually let me color code it just so you see what we're doing. I want to be very careful with this math so that nothing seems too confusing. Although this is really just algebraic manipulation. So if I add all of these up, I get y1 squared plus y2 squared all the way to yn squared. I'll put some parentheses around that. And then to that, we have these common terms.