x+y=-14.(1)
y+z=-7 .(2)
x+z=19.(3)
三式相加,得
2x+2y+2z=-2
x+y+z=-1.(4)
(4)-(1)得
z=13
(4)-(2)得
x=6
(4)-(3)得
y=-20
解得
x=6
y=-20
z=13