已知2x+5y+4z=15.7x+y+3z=14 则x+y+z=?

问题描述:

已知2x+5y+4z=15.7x+y+3z=14 则x+y+z=?


a(2x+5y+4z)+b(7x+y+3z)=x+y+z
比较系数得
2a+7b=5a+b=4a+3b=1
a=1/11,b=2/11
因此
x+y+z=a(2x+5y+4z)+b(7x+y+3z)
=1/11(2x+5y+4z)+2/11(7x+y+3z)
=15/11+28/11
=43/11