This error right over here is going to be y2 minus mx2 plus b, so y2. And then this right here, this point right here, is mx2 plus b, the value when you take x2 into this line. And then we keep going all the way to our nth point. This error right here is going to be yn minus mxn plus b. Now, what we want to do, so if we wanted to just take the straight up sum of the errors, we could just sum these things up. But what we want to do is minimize the square of the error between each of these points, each of these end points in the line. So let me define, I'll do this in a new color.