若3x+5y+z=0,3x+y-7z=0则x+y-z的值等于 ( )
来源:百度知道 编辑:UC知道 时间:2024/06/05 14:58:13
(A)1 (B)0 (C)2 (D)不能求出
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0.式子相加,可得到x=z.y=-2z.所以要求的正好是0,跟具体xyz 是几无关!
B
B
两式相减得4y+8z=0
即y=-2z
从而x+y-z=x-3z
然后(3x+5y+z)-5*(3x+y-7z)=-12x+36z=0
得x+y-z=x-3z=0
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