The sum of all of this stuff right over here is the same thing as this term right over here. And then we have to sum this right over here. And you see again, we can factor out. We can factor out here a minus 2b out of all of these terms. So we have minus 2b times y1 plus y2 plus all the way to yn. So this business, so these terms right over here, these terms right over here when you add them up, give you these terms or this term right over there. And let's just keep going.