x-2y+z=9 (1)
3x+2y-2z=4 (2)
2x-z=9 (3)
(1)+(2)
4x-z=13 (4)
(4)-(3)
2x=4
所以
x=2
z=2x-9=-5
y=(x+z-9)/2=-6
x-2y+z=9 3x+2y-2z=4 2x-z=9
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