5x+5y-8z=13 (1)
6x+4y-z=9 (2)
2x+3y-4z=5 (3)
(1)-(3)×2
x-y=3 (4)
(2)×4-(3)
22x+13y=31 (5)
(4)×13+(5)
35x=70
所以
x=2
y=x-3=-1
z=6x+4y-9=-1