等差数列(an),(bn)的前n项和为Sn,Tn,且Sn/Tn=2n/3n+1,则a8/b8=?
问题描述:
等差数列(an),(bn)的前n项和为Sn,Tn,且Sn/Tn=2n/3n+1,则a8/b8=?
答
a8/b8=(a1+a15)/(b1+b15).等差中项
S15=15*(a1+a15)/2
T15=15*(b1+b15)/2
a8/b8=S15/T15
=2*15/3*15+1
=15/23