V=23πr3V = \frac{2}{3} \pi r^{3}V=32πr3
dVdr=2πr2\frac{dV}{dr} = 2\pi r^{2}drdV=2πr2
dVdr(r=2)=2π(2)2\frac{dV}{dr}(r=2) = 2\pi (2)^{2}drdV(r=2)=2π(2)2
= 8π8\pi8π
