若xyz不等于0,且x+2y-7z=0,4x-3y-6z=0,求x+2y+z/x-2y-z的值?

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若xyz不等于0,且x+2y-7z=0,4x-3y-6z=0,求x+2y+z/x-2y-z的值?
若xyz不等于0,且x+2y-7z=0,4x-3y-6z=0,求x+2y+z/x-2y-z的值?

若xyz不等于0,且x+2y-7z=0,4x-3y-6z=0,求x+2y+z/x-2y-z的值?
由已知:
x+2y-7z=0 (1)
4x-3y-6z=0 (2)
将(2)*4-(1)*5得:11x-22y+11z=0,即:x-2y+z=0
(x+2y+z)/(x-2y-z)
=(x+2y-7z+8z)/(x-2y+z-2z)
=8z/(-2z)
=-4
如想知道:(2)*4-(1)*5我是怎么想出来的,