Do you know Pappus' Theorem? .Did you make a sketch?
Use Pappus's Theorem to find the volume of the torus obtained
when the region inside the circle is revolved about the line
Pappus' Theorem . . . The volume of a solid of revolution is equal to:
the area of the region times the distance travled by its center of mass.
The area of the circle is . .The center of mass is its center.
The distance travelled is the circumference of a circle with radius
Therefore, the volume is: .