已知2x+5y+4z=15,7x+y+3z=14,则4x+y+2z的值为_.

问题描述:

已知2x+5y+4z=15,7x+y+3z=14,则4x+y+2z的值为______.

由于2x+5y+4z=15,7x+y+3z=14;
令4x+y+2z=m(2x+5y+4z)+n(7x+y+3z)=(2m+7n)x+(5m+n)y+(4m+3n)z;
由于左边=右边,则可列方程组

2m+7n=4
5m+n=1
4m+3n=2
;解得:
m=
1
11
n=
6
11

因此4x+y+2z=m(2x+5y+4z)+n(7x+y+3z)=
1
11
×15+
6
11
×14=9.
故答案为:9.