at(-1,2,3)z^2=16-3x^2-y^2dz/dx=(-6x)/(2 \sqrt(16-3x^2-y^2) )=1dz/dy=(-2y)/(2 \sqrt(16-3x^2-y^2))=-2/3切平面:(z-3)=1(x+1)+(-2/3)(y-2)3x-2y-3z+16=0\lambda=-2.
