因为4（2x+5y+4z）+6（3x+y-7z）=4×6+6×（-4）=0，
所以4（2x+5y+4z）+6（3x+y-7z）=26（x+y-z）=0，
所以x+y-z=0．
若2x+5y+4z=6，3x+y-7z=-4，那么x+y-z的值是多少？
若2x+5y+4z=6，3x+y-7z=-4，那么x+y-z的值是多少？
数学人气：650 ℃时间：2019-09-11 11:48:34
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