切点是(-1,2,1),求导x'=3t²,y'=1,z'=2t，t=-1时x'=3,y'=1,z'=-2,所以切线方程为(x+1)/3=(y-2)/1=(z-1)/-2.法平面方程为3(x+1)+1(y-2)-2(z-1)=0即3x+y-2z+3=0
