[คุณชายน้อย]

$$\int_0^1\!\!\!\int_0^\sqrt{1-x^2}\!\!\!\int_0^\sqrt{1-x^2-y^2} \frac{dzdydx}{\sqrt{1-x^2-y^2-z^2}}~(รูป A)~=~\int_0^{\frac{\pi}{2} }\!\!\!\int_0^{\frac{\pi}{2} }\!\!\!\int_0^1 \frac{\rho ^2 sin~\phi }{\sqrt{1-\rho ^2}}d\rho d\phi d\theta ~(รูป B)~=\frac{{\pi}^2}{8} $$