设等差数列{an}与{bn}的前n项之和为Sn,S`n,Sn/S`n=7n+2/n+3,求a7/b7

问题描述:

设等差数列{an}与{bn}的前n项之和为Sn,S`n,Sn/S`n=7n+2/n+3,求a7/b7

因为{an}是等差数列,所以2a7=a6+a8,2b7=b6+b8
即S13=13a7,S`13=13b7
所以a7/b7=S13/S`13=(7*13+2)/(13+3)=93/16