x=arcosz，y=brsinz，J=D(x，y)/D(r，z)=abr。
The integral function is ab (1-r 2) 0.5 * r, 0.
Obviously, the angle integral is 2π.
That is, from 0- 1 product ∫∫ (1-r 2) * rdr, the first method of substitution is used to convert it into-abπ∫∫ (1-r 2) d (/kloc-0). The result of integration is 3abπ/2.