I've been looking at this method here: http://planetmath.org/encyclopedia/6668.html [Broken] I was wondering at the last step before the "Note on multi-valuedness" if you wanted to obtain the general formula for the surface area of a sphere [tex]4 \times \pi \times r^2[/tex] with a radius of well r what limits would you use for each of the integrations? Well i say each of the integrations it looks like only one there (only one integration sign) but with the dx and dy after it does that mean it can be split up into two integrations? If so I don't understand where the [tex] \pi [/tex] comes from? I mean i'm guessing the f(x,y) and z cancel leaving just the r is that right? Sorry if this is a silly question!