The following shows a solid being created with a cylindrical shell inside to help visualize how the volume can be computed by means of cylindrical shells.
The figure may be rotated by dragging the cursor across the figure (while holding the mouse button). The figure will continue to rotate if one releases the mouse button while still moving the figure.
You may change the top and bottom equations, the left and right endpoints (a and b), and the line of rotation given above the figure to obtain a new figure.