x-4y-z=-3①
2x+y-z=18②
x-y-z=6③
(3)-(1)得;3y=21,y=7
(2)-(3)得:x+2y=12(4)
将y=7带入(4)得:x+14=12,x=-2
将x=-2,y=7带入(3)得;-2-7-z=6,z=-15
所以方程组的解为x=-2,y=7,z=-15
x-4y-z=-3①
2x+y-z=18②
x-y-z=6③
(3)-(1)得;3y=21,y=7
(2)-(3)得:x+2y=12(4)
将y=7带入(4)得:x+14=12,x=-2
将x=-2,y=7带入(3)得;-2-7-z=6,z=-15
所以方程组的解为x=-2,y=7,z=-15