1种情况x,y,z均为0
2种情况x,y,z不为0
设xy=z-x-y 1
xz=y-x-z 2
yz=x-y-z 3
1+2 y+z=-2
1+3 x+z=-2
2=3 y+z=-2
得x=-1 y=-1 z=-1