已知xyz不等于0,x+3y+z=0,2x+3y-z=0,则x+2y-7z / 3x+5y+z的值为___?

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已知xyz不等于0,x+3y+z=0,2x+3y-z=0,则x+2y-7z/3x+5y+z的值为___?已知xyz不等于0,x+3y+z=0,2x+3y-z=0,则x+2y-7z/3x+5y+z的值为

已知xyz不等于0,x+3y+z=0,2x+3y-z=0,则x+2y-7z / 3x+5y+z的值为___?
已知xyz不等于0,x+3y+z=0,2x+3y-z=0,则x+2y-7z / 3x+5y+z的值为___?

已知xyz不等于0,x+3y+z=0,2x+3y-z=0,则x+2y-7z / 3x+5y+z的值为___?
解 :x+3y+z = 0 ①
2x+3y-z = 0 ②
① + ② 得 3x +6y =0 即 x +2y =0 y= -0.5x
② - ① 得 x – 2z =0 z = 0.5x
(x+2y-7z)/(3x+5y+z)
=(x+2y-7z)/(3x+6y-y+z)
=(-7z)/(-y+z)
=(-7×0.5x)/(0.5x+0.5x)
=(-3.5x)/x = -3.5

x+3y+z=0
2x+3y-z=0
两式相加得出3x+6y=0即x+2y=0
两式相减得出x-2z=0即x=2z,
由新得出的两式可知y=-z
把x+2y=0,x=2z,y=-z代入要求解的式子得出
-7z/2z等于-3.5
完毕~~