And then finally, the partial derivative of this with respect to b is going to be 2nb, or 2nb to the first. You could even say 2bn, or 2nb is the partial derivative of that with respect to b. And we want to set this equal to 0. So it looks very complicated, but remember we're just trying to solve for the m's and the b's. And we have two equations with two unknowns here. We have the m's, we have the m's, and then we have the b's. And to simplify this, both of these equations, actually the top one and the bottom one, both sides are divisible by 2n.