Sketch the axis of rotation (flag pole) then use washers.
Note the x represents the length of the radius, it's part of the
equation. And represents the height of each shell.
Refer to the hint in part (a).
and represent radii of an outer and inner solid (the 'inner' solid is the hole). Make the function with the longer radii and the function with the shorter radii. Note: It is possible that is below on the graph. Once rotation happens, this will switch.
Also note that both radii have different lengths than
and , since the axis of rotation is units above the -axis. Adjust the integral in part (a) accordingly:
As in part (b), to avoid using horizontal rectangles (and rewriting the integrand in terms of
), you can use shells.
The setup should look exactly like the setup in part (b), with one exception: The radii are no longer the same values as the bounds. They will be either longer or shorter than the bounds. So shift the radii
units to the left or right: