We're going from x equals 1 to x equals 4, and we're essentially taking this area, one way to think about it, between our square root of x and 1, and we're rotating it around 1. We're using these little disks right over here, so the interval between 1 and 4. This is going to give us the volume of our solid of revolution. Now we just have to evaluate this definite integral. Let's give a shot at it. This is going to be equal to the integral from 1 to 4, and we can factor out, or we can put the pi outside the integral sign, and then we can expand this out. Square root of x squared.