两个等差数列{an}和{bn}的前n项和分别为Sn和Tn,若SnTn=7n+3/n+3,则a8b8=_.
问题描述:
两个等差数列{an}和{bn}的前n项和分别为Sn和Tn,若
=Sn Tn
,则7n+3 n+3
=______. a8 b8
答
∵
=Sn Tn
7n+3 n+3
∴
=a8 b8
=2a8
2b8
=
a1+a15
b1+b15
(a1+a15)15 2
(b1+b15)15 2
=
=S15 T15
=67×15+3 15+3
故答案为:6