dx/dt = e^t cost, dy/dt = 2cost-sint, dz/dt = 3 e^3t在t=0处,点的坐标（0,1,2），切向量 S = {1,2,3}切线 x/1=（y-1)/2 =（z-2)/3法平面 1*x+2*(y-2)+3(z-2)=0
