设等差数列{an}的前n项和为Sn,若a5=5a3,则S9S5=_.

问题描述:

设等差数列{an}的前n项和为Sn,若a5=5a3,则

S9
S5
=______.

∵{an}为等差数列,
S9=a1+a2+…+a9=9a5,S5=a1+a2+…+a5=5a3

S9
S5
9a5
5a3
=9
故答案为9