由已知得 |z| = √[(x-1)^2+(y+1)^2+(z-2)^2] , 平方得 z^2 = (x-1)^2+(y+1)^2+(z-2)^2 , 化为 (x-1)^2+(y+1)^2-4(z-1) = 0 .这就是 M 的轨迹方程.
