若3x+7y+z=5,4x+10y+z=3,则x+y+z=?

问题描述:

若3x+7y+z=5,4x+10y+z=3,则x+y+z=?

3x+7y+z=5.(1)
4x+10y+z=3.(2)
(1)*3-(2)*2得
x+y+z=15-6=9
所以x+y+z=9