It's equal to xn minus 1 plus delta x. So now I think we've set up all of the notation and all of the conventions in order to actually calculate the area or our approximation of the area. So our approximation, approximate area, is going to be equal to what? Well, it's going to be the area of the first rectangle. So let me write this down. So it's going to be rectangle 1, so the area of rectangle 1, so rectangle 1 plus the area of rectangle 2, plus the area of rectangle 2, plus the area of rectangle 3. I think you get the point here.