若x/3=y/4=z/5则x+y/x-2y+3z=?

问题描述:

若x/3=y/4=z/5则x+y/x-2y+3z=?

设x/3=y/4=z/5=k(k≠0)
则x=3k,y=4k,z=5k,代入(x+y)/(x-2y+3z),得
(x+y)/(x-2y+3z)=(3k+4k)/(3k-2×4k+3×5k)=7k/10k=7/10