x+y-z=6(1)
x-3y+2z=1 (2)
3x+2y-z=8 (3)
(1)×2+(2)
3x-y=13 (4)
(3)-(1)
2x+y=2 (5)
(4)+(5)
5x=15
所以
x=3
y=2-2x=-4
z=x+y-6-7