[tex3]
\begin{align}
V&=\int_{-\frac{\pi}{36}}^{\frac{\pi}{36}}\pi\left([f(x)]^2-81\sec^2(9x)\right)\mathrm{d}x\\
&=\pi\left(\int_{-\frac{\pi}{36}}^{\frac{\pi}{36}}[f(x)]^2\mathrm{d}x -\int_{-\frac{\pi}{36}}^{\frac{\pi}{36}}81\sec^2(9x)\mathrm{d}x\right)\\
&=\pi\left(54 -9\left[\tan(9x)\right]_{\!-\!\frac{\pi}{36}}^{\,\frac{\pi}{36}}\right)\\
&=\pi\left(54-9\tan(\dfrac{\pi}{4})+9\tan(-\dfrac{\pi}{4})\right)\\
&=\pi\left(54-9\cdot2\tan(\frac{\pi}{4})\right)\\
&=36\pi
\end{align}
[/tex3]
[tex3]
\boxed{\hspace{0.5cm}\\[8pt]\hspace{0.5cm}\alpha=36\hspace{0.5cm}\\\hspace{0.5cm}}\\
[/tex3]