不是曲面积分。是积分求旋转面.
jinjing
2011-08-15 16:26:28
( reads)
A=intg(2pi*x*ds)=intg(2pi*x*sqt(1+(dx/dy)^2)dy=intg2pi*x*sgt(1+y^2/x^2)dy=intg(2pi*sqt(x^2+y^2)dy=intg2pi*Rdy from 0 to h, So,A=2piRh.
x^2+y^=R, so.dx/dy=-y/x. So,ds=sqt(1+(dx/dy)^2*dy=...