I've done this problem, however not in the way suggested (which I assume is much quicker and easier!)

By evaluating an appropriate double integral, ﬁnd the volume of the wedge lying between the planes $\displaystyle z=px$ and $\displaystyle z = qx$ ($\displaystyle p > q > 0$) and the cylinder $\displaystyle x^2 + y^2 = 2ax$

(where $\displaystyle a > 0$)

I did it by switching to cylindrical polars and then doing the triple integral as I couldnt see a method using a double integral to get the answer $\displaystyle V=\pi (p-q)a^3$

Using the integral

$\displaystyle \int_{\phi=-\pi/2}^{\pi/2} \int_{r=0}^{2a\cos \phi} \int_{z=qr \cos \phi}^{pr \cos \phi} r dz dr d \phi$

any help with doing this with a better method?