So this error right here, error 1, if you think about it, it is this value right here, this y value. It's equal to y1 minus this y value. Well, what's this y value going to be? Well, over here we have x is equal to x1. And this point is the point mx1 plus b. You take x1 into this equation of the line, and you're going to get this point right over here. So that's literally going to be equal to mx1 plus b.