作业帮2x+3y-4z=0,3x+4y+5z=0,求x+y-z/x-y+z的值
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2x+3y-4z=0,3x+4y+5z=0,求x+y-z/x-y+z的值
2x+3y-4z=0,3x+4y+5z=0,求x+y-z/x-y+z的值
2x+3y-4z=0,3x+4y+5z=0,求x+y-z/x-y+z的值
2x+3y-4z=0,
3x+4y+5z=0
两式把z看作已知,可解得
x=-31z
y=22z
(x+y-z)/(x-y+z)=(-31z+22z-z)/(-31z-22z+z)=5/26
做一个2元一次方程不就行了
设x+y-z=a;x-y+z=b.则x=(a+b)/2;y=(a-b+2z)/2
代入已知条件得：
5a-b=2z……(1)
7a-b=-2z……(2)
(1)+(2)得：12a-2b=0
=>a/b=1/6
即x+y-z/x-y+z的值为 1/6
2x+z=10 x+y-z=4 3x-y-z=0
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1.{x:y:z=3:4:5 2x+3y-5z=-142.{x-y-z=-1 3x+5y+7z=11 4x-y+2z=-13.{x+y=1 x+z=0 2x+y+2z=44.{x-y+z=-3 2x-y-z=-2 -3x+y+z=-15.{x-y+z=-3 3x+y-4z=6 2x+y-z=36.{x-2y+5z=16 2x+y-5z=7 2x-y+z=38
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