Let ∑ be the area enclosed by a closed curve L. According to Green's formula ∫ L (y 3-y) dx-2x 3dy = ∫ (-6x 2-3y 2+1) dxdy, let's look at m = ∫ ∫ (. To maximize the volume, you only need to get as large as possible z & gt=0. So, take all the parts where Z =-6x 2-3Y 2+ 1 is on the xoy plane. Therefore, as long as ∑ is -6x 2-3y 2+ 1