If two solids have cross sections of equal area for all horizontal slices, then the have the same volume.
Therefore the volume of the hemisphere
= volume of cylinder - volume of cone
= (π R3) - (1/3) (π R3)
= (2/3) (π R3)
The volume of the sphere is twice that.
as 2 complet hemispher makes 1 complet spher
So it is (4/3)(π R3).