Using cylindrical shells is an easier method of finding volumes when the previous methods become too difficult to solve. For example, consider a problem with a solid obtained by rotating about the y-axis, the region bounded by  and. If you use the washer method, you would have to solve the cubic equation For x in terms of y; that’s difficult.

 Rotate about y-axis

 Rotate about x=2

Here are some links to some helpful websites on Cylindrical Shells.

Link to letters of advice.

Letters