1)如果X+Y+Z不=0.
y+z/x = z+x/y = x+y/z =k
前面3式分子,分母相加.
2（x+y+z)/(x+y+z)=k
k=2
2)如果X+Y+Z=0.
y+z=-x,x+y=-z,z+x=-y
k=-1.