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. Now what I want to do is kind of come up with a more meaningful estimate of how good this line is fitting the data points that we have. To do that, we're going to ask ourselves the question, how much, or we could even say what percentage, what percentage of the variation in y is described by the variation in x? And so let's think about this.