Question

Here is an non-specific question concerning calculus, when finding the region bounded by the curves or whatever the equations are, find the volume of the solid obtained by revolving about whatever axis. When doing these type of problems, when exactly do you use 2pi in the beginning of the integral and when do you not? Sorry if this is confusing, hopefully you know what I'm talking about!

Answer 1

Only when using the cylindrical shell method.. so basically when your dx or dy slices are parallel to the axis you're rotating about. when it's perpendicular use pi r^2