If we have to find the volume, written in polar cordinates, inside this sphere X2+y2+z2=16 and outside this cylinder x2+y2=4 How should I approach this? Could I take the sphere function and reqrite in polar cordinates z=√(16-X2-y2) which is the same as z=√(16-r2) But then I have to make r depend on a function of the cylinder right? so x2+y2=4 ---> r2=4 so r=2 this must be the boundaries of the cylinder.. Now I get a bit confused. Do we subtract the sphere function from the cylinder function? Or do we make the cylinder function a function that r depends on?