 Pappus's centroid theorem - The second theorem: Encyclopedia II - Pappus's centroid theorem - The first theoremThe first theorem states that the surface area A of a surface of revolution generated by rotating a plane curve C about an axis external to C and on the same plane is equal to product of the arc length s of C and the distance d1 traveled by its centroid.
For example, the surface area of the torus with minor radius r and major radius R is
...
See also:Pappus's centroid theorem, Pappus's centroid theorem - The first theorem, Pappus's centroid theorem - The second theorem Read more here: » Pappus's centroid theorem: Encyclopedia II - Pappus's centroid theorem - The first theorem | 
