若2x+5y+4z=6,3x+y-7z=—4,求x+y-z

问题描述:

若2x+5y+4z=6,3x+y-7z=—4,求x+y-z
补加20分

一式各乘以3减掉二式乘以2,得到y+2z=2,
二式乘以5减掉一式,得到x-3z=-2,
x+y-z=0