In order to calculate the volume of a solid of revolution, you can either use the int command implementing the formula above or use the Maple procedure RevInt which sets up the integral for you. Try the examples below to see the different types of output.
> Pi*int(f(x)^2,x=-2..2); > evalf(Pi*int(f(x)^2,x=-2..2)); > RevInt(f(x),x=-2..2); > value(RevInt(f(x),x=-2..2)); > evalf(RevInt(f(x),x=-2..2));