Find volume of revolution using disk/washer method (#575)

Find volume of revolution using disk/washer method (#575)

For rotation about xx-axis: V=π∫ab[f(x)]2 dxV = \pi \int_a^b [f(x)]^2 \, dx; washer: π∫ab([f(x)]2−[g(x)]2) dx\pi \int_a^b ([f(x)]^2 - [g(x)]^2) \, dx.