Hello, thedoge!

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: .