计算∫cz^3ds,其中C为圆锥螺旋线:x=tcost,y=tsint,z=t,0
问题描述:
计算∫cz^3ds,其中C为圆锥螺旋线:x=tcost,y=tsint,z=t,0
答
求导:x'=cost-tsint,y'=sint+tcost,z'=1ds=√[(x')^2+(y')^2+(z')^2]dt=√(2+t^2)dt∫z^3ds=∫(0到√2) t^3√(2+t^2)dt(换元u=t^2)=1/2×∫(0到2) u√(2+u)du=1/2×∫(0到2) [√(2+u)^3-2√(2+u)]du,√...