设:球的体积V,半径R,将球划分成n个圆柱体,每个圆柱体的半径为r,高为h(微元dh),底面积为s,体积为v,有
$
\begin{flalign}
&h=R\cdot{sinθ} \\
&r=R\cdot{cosθ} \\
&s=πr^2 \\
&v=s×h=πr^2×R\cdot{sinθ}=π{(R\cdot{cosθ})^2}×R\cdot{sinθ}
\end{flalign}
$
$
\begin{flalign}
V&=2\int_{0}^{R}sd_h=2\int_{0}^{R}πr^2d_h=2\int_{0}^{π/2}π(R\cdot{cosθ})^2d_{(R\cdot{sinθ})} \\
&=2πR^3\int_{0}^{π/2}cos^2θd_{sinθ}\\
&=2πR^3\int_{0}^{π/2}(1-sin^2θ)d_{sinθ}\\
&=2πR^3\left(\int_{0}^{π/2}d_{sinθ}-\int_{0}^{π/2}sin^2θd_{sinθ}\right)\\
&=2πR^3\left[sinθ-\frac{1}{3}sin^3θ\right]_{0}^{π/2} \\
&=2πR^3(1-\frac{1}{3})\\
&=\frac{4}{3}πR^3
\end{flalign}
$