设Sn是等差数列{an}的前n项和，若a7a4＝2，则S13S7的值为267267．

Question

设S_n是等差数列{a_n}的前n项和，若(a7)/(a4)＝2，则(S13)/(S7)的值为

(26)/(7)

(26)/(7)

．

Answer 1

由题意可得(S13)/(S7)=((13(a1+a13))/(2))/((7(a1+a7))/(2))=(13(a1+a13))/(7(a1+a7))
=(13×2a7)/(7×2a4)=(13)/(7)×(a7)/(a4)=(13)/(7)×2=(26)/(7)．
故答案为：(26)/(7)