Is there a simple or generalized way (formula) to generate the radius of a solid of revolution? How does the orientation of the function relative to the axis of revolution affect the radius (radius= 4-f(x) or 4+f(x))? Why is the radius sometimes only x or y , and other times some other function? I consistently get the radius wrong in the solid of revolution problems with non-zero axis, and don't know if its a conceptual problem or that I just never learned the correct way to determine the radius. Thank you.