And if I wanted to find the volume of this entire solid, this entire rotated solid, I would want to find the sum of all of these volumes. So this is just the disk right over here, but I could have another disk, a similar disk that I do right over here. I could have another disk right over here. And I want to take the sum of all of those disks. So I want to take, so the volume is going to be the sum over all of those disks. So x goes from zero, which is this bounding point, to x is equal to 1 1⁄2, times pi times one minus f of x squared. This is the area of the face of each of those disks.