So, I know the formula for the disc method is: $\displaystyle v=pi\int\limits_{b}^{a}[R(x)]^2dx$ ...what I'm so confused about is how to fix up $\displaystyle [R(x)]$ when the axis of revolution isn't the x-axis or the y-axis. For example:

What is the equation to be used when using the disc method to get:

a.) shaded region when revolved to y=8

b.) non-shaded region when revolved to y=8

Thank you in advance!