Calculating ∫ f d A {\displaystyle \int fdA} and ∫ f d V {\displaystyle \int fdV} with angular symmetry Cyndrical: d A = 2 π r d z ; d V = d A d r {\displaystyle dA=2\pi r\,dz;\,dV=dA\,dr} . Spherical: ∫ d A = 4 π r 2 , d V = 4 π r 2 d r {\displaystyle \int dA=4\pi r^{2},\;dV=4\pi r^{2}\,dr}
