已知xyz不等于0,且x+2y-z=0,7x-y-z=0,求x+y+z/2x-y-z的值.

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已知xyz不等于0,且x+2y-z=0,7x-y-z=0,求x+y+z/2x-y-z的值.
已知xyz不等于0,且x+2y-z=0,7x-y-z=0,求x+y+z/2x-y-z的值.

已知xyz不等于0,且x+2y-z=0,7x-y-z=0,求x+y+z/2x-y-z的值.
因为x+2y-z=0,7x-y-z=0
两式相减,得:6x-3y=0,
所以y=2x
代入x+2y-z=0中,
得:x+4x-z=0,
那么z=5x
那么(x+y+z)÷(2x-y-z)
=(x+2x+5x)÷(2x-2x-5x)
=(8x)÷(-5x)
=-8/5

x+2y-z=0 得z=x+2y
代入 7x-y-z=0 得 6x-3y=0
得 y=2x
代入 z=x+2y
得z=5x
于是 x+y+z/2x-y-z = (x+2x+5x)/(2x-2x-5x) = 8x/-5x = -8/5