已知3x+7y+4z=35,x+5y+2z=40,则x+y+z=_.

问题描述:

已知3x+7y+4z=35,x+5y+2z=40,则x+y+z=______.

将两式组成方程组得

3x+7y+4z=35
x+5y+2z=40

①-②得,2x+2y+2z=-5,
∴x+y+z=-
5
2

故本题答案为:-
5
2