1. The problem statement, all variables and given/known data Hi, well, I don't have to solve any problem yet. I have an inquietude about solids of revolution. I've been reading this: http://en.wikipedia.org/wiki/Solid_of_revolution and this: http://en.wikipedia.org/wiki/Disk_integration What I wanted to know is if its the same this equation than the other: This one: And this one: I think I'm getting it now... The second one is to derive the function under the curve (or between the curve and the X axis) around the Y axis, and the first derives between the curve and the Y axis around the Y axis. Is that right? Bye, and thanks off course.