Question

Your friend claim that if you rotate around the given axis, the composite solid will be made of a right circular cylinder and a cone.

a. Is your friend correct
b. Explain your reasoning

Answer 1

The friend is correct. Split the 2D figure as indicated in the diagram below. The rectangle on the left rotates to form the cylinder. The triangle rotates to form the cone. Think of these as like a revolving door that carves out a 3D shape. Or you could think of propellers.