3x+2y=7 2x+5y=1 2x-y+3z=25

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3x+2y=7 2x+5y=1 2x-y+3z=25
三元一次!

3x+2y=7 (1)
2x+5y=1 (2)
2x-y+3z=25 (3).
由(1)*2-(2)*3得：
-11y=11.
y=-1.
3x-2*1=7.
3x=9.
x=3.
将x=3,y=-1代入(3):
2*3-(-1)+3z=25.
3z=25-7.
3z=18.
z=6.
∴x=3,
y=-1,
z=6.

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