已知x=y/3=z/5,xyz≠0,求(x-3y+5z)/(x+3y-5z)的值

题目

已知x=y/3=z/5,xyz≠0,求(x-3y+5z)/(x+3y-5z)的值

答案

由x=y/3=z/5,得x:y:z=1:3:5
设x=a,y=3a,z=5a
(x-3y+5z)/(x+3y-5z)
=(a-9a+25a)/(a+9a-25a)
=-17/15