And so what we're going to do is attempt to do this using, I guess you could call it the washer method, which is a variant of the disk method. So let's construct a washer. So let's look at a given x. So let's say an x right over here. So let's say that we're at an x right over there. And what we're going to do is we're going to rotate this region. We're going to give it some depth, dx.