Select an example or define a function [math]f[/math] between [math]a[/math] and [math]b[/math]. The area between the [math]x[/math]-axis and the graph of [math]f[/math] can then be rotated about the [math]x[/math]-axis.[br][br]The cross-section at [math]x[/math] is a circle of radius [math]f\left(x\right)[/math]. Its area is [math]A\left(x\right)=\pi\left[f\left(x\right)\right]^2[/math].[br][br]The volume of the solid is [math]V=\int_a^bA\left(x\right)dx=\int_a^b\pi\left[f\left(x\right)\right]^2dx[/math].