That's the inside of our three-dimensional surface. We want to find the m and b values that minimize the value on the surface. There's some m and b value right over here that minimizes it. To do that, and I'll actually do the calculation in the next video, we're going to find the partial derivative of this with respect to m, and we're going to find the partial derivative of this with respect to b and set both of them equal to zero. Because at this minimum point, I guess you could say in three dimensions, this minimum point on the surface is going to occur is when the slope with respect to m and the slope with respect to b is zero. At that point, the partial derivative of our squared error with respect to m is going to be equal to zero, and the partial derivative of our squared error with respect to b is going to be equal to zero. All we're going to do in the next video is take the partial derivative of this expression with respect to m, set that equal to zero, and the partial derivative of this with respect to b, set that equal to zero, and then we're ready to solve for the m and the b, or the particular m and b.