若2x+5y-4z=0,3x+9y-7z=0,则x+y-z的值为

问题描述:

若2x+5y-4z=0,3x+9y-7z=0,则x+y-z的值为

2x+5y-4z=0,.(1)
3x+9y-7z=0.(2)
(2)-(1),得
x+4y-3z=0.(3)
(1)-(3),得
x+y-z=0
所以
x+y-z的值为0