It's essentially our function minus what we are rotating around. That gives us the radius, and so this will give us the area of each of our faces, and then we just multiply that times the depth. The depth, of course, is dx. We've done that multiple times, so times dx. This is the thing that we want to sum up. This is the thing that we want to sum up over our interval. Our interval, let's see, this point right over here where the square root of x is equal to 1, that's just going to be x equals 1.