I know the formula of sphere and have seen number of derivations using with and without calculus.
I was using a common sense approach of using a slice and rotating this slice 360deg. Number of such slices would be 2(pi)(r) which is length of base circle of hemi-sphere. Then we can multiply the volume by 2 to get volume of entire sphere. I am using same logic as used for volume of a cylinder which is using a small slice and using number of such slices as height of the cylinder which is also its length.
What is wrong with my approach ?