This length right over here is square root of x minus 1 for any given x in our interval. So it's going to be equal to square root of... Let me do that same orange color just to make it clear where I'm getting it from. It's going to be equal to square root of x minus 1. 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.