h

\varphi

\frac{4h^{3}\tg^{2}\frac{\varphi}{2}}{3\left(1-\tg^{2}\frac{\varphi}{2}\right)}=\frac{2}{3}h^{3}\tg\varphi\tg\frac{\varphi}{2}=\frac{4h^{3}\sin^{2}\frac{\varphi}{2}}{3\cos\varphi}