So if you were to visualize it over here, you have some depth. And when you rotate it around, the inner radius is going to look like the inner radius of our washer is going to look something like that. And then the outer radius of our washer is going to contour around x squared minus 2x. So it's going to look something like that. And of course, our washer is going to have some depth. So let me draw the depth. So it's going to have some depth, dx.