Chapter 14.6, Problem 4ES

Evaluate the iterated integral.

${\displaystyle {\int }_0^{2\pi }{\displaystyle {\int }_0^{\pi /4}{\displaystyle {\int }_0^{a\sec \varphi }{\rho }^2\sin \varphi d\rho d\varphi d\theta }}}\left(a>0\right)$