Clearly, the way I've drawn it right over here for the function we're using, it's going to be an underestimate because we've given up all of that pink area that I had colored in before. It's an underestimate, but it's an approximation of the area under the curve. In the next few videos, we're going to try to generalize this to situations where we have an arbitrary function and we have an arbitrary number of rectangles. And we'll also start, in videos after that, we'll look at rectangles where we define the height not by the left boundary, but by the right boundary, or by the midpoint. Or maybe we don't use rectangles at all. Maybe we might use things like trapezoids. Anyway, have fun.