x+y+z=4 (1)
2y+z=0 (2)
3x+2y-4z=-1 (3)
(1)×3-(3)
y+7z=13 (4)
(4)×2-(2)
14z-z=26-0
13z=26
所以
z=2
y=13-7z=-1
x=4-y-z=3