20 14 there is something I don't understand about the problem of finding the volume of the rotating body in the second part of the postgraduate mathematics.
At this point, I believe you have found f(x, y). The area surrounded by f(x, y)=0 is the projection of the curve f(x, y) on the xoy plane. Regardless of its shape, the differential element method is used to take dx as the height of the rotating body and the radius as the distance from the point on the curve to the straight line y=- 1. That is, the distance from the projection y on the xoy plane to the straight line y=- 1, so you will know. The square of radius r = (y+ 1).