That is error 1, and we want the squared errors between each of the points in the line. So that's the first one. Then you do the same thing for the second point. So we started our discussion this way, y2 minus mx2 plus b squared all the way, I'll do dot, dot, dot to show that there are a bunch of these that we have to do until we get to the nth point, all the way to yn minus mxn plus b squared. Now that we actually know how to find these m's and b's, I showed you the formula, in fact we've proved the formula of how to find these m's and b's. We can find this line, and if we wanted to say, well, you know, how much error is there, we can then calculate it because we now know the m's and the b's. So we can calculate it for a certain set of data.