Volumes of revolution are found by integration just as two-dimensional areas are, only our cross-sections are discs or hollow cylinders (called 'shells') instead of rectangles.

We can find the answer to the first problem by rewriting the function as

and using the Shell Method. To do this, we note that the radius of each shell is

and the height

. The volume of each cross section will therefore be

Integrating from

to

, we obtain

(Actually, the correct way to rewrite the function is

, but we accounted for both sides in our integral.)

For the second problem, the volume is infinite. Are you sure it's written correctly?