kx+y=1
ky+z=1
kz+x=1
kx+y+ky+z+kz+x=3
kx+ky+kz+x+y+z=3
k(x+y+z)+x+y+z=3
(k+1)(x+y+z)=3
方程组无解
k+1=0
k=-1