2x+5y+4z=0 ,3x+y-7z=0,则x+y-z的值为多少?

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2x+5y+4z=0,3x+y-7z=0,则x+y-z的值为多少?2x+5y+4z=0,3x+y-7z=0,则x+y-z的值为多少?2x+5y+4z=0,3x+y-7z=0,则x+y-z的值为多少?2

2x+5y+4z=0 ,3x+y-7z=0,则x+y-z的值为多少?
2x+5y+4z=0 ,3x+y-7z=0,则x+y-z的值为多少?

2x+5y+4z=0 ,3x+y-7z=0,则x+y-z的值为多少?
2x+5y+4z=0(1)
3x+y-7z=0 (2)
(1)*3-(2)*2消去x,得13y-26z=0,得y=2z;
(2)*5-(1)消去y,得13x-39z=0,x=3z;
所以,x+y-z =3z-2z-z=0.

2x+5y+4z=0, 3x+y-7z=0.
x+y-z
=(2/13)*(2x+5y+4z)+(3/13)*(3x+y-7z)=0.