等差数列{an},{bn}的前n项和分别为An,Bn,且AnBn=7n+45n+3,则a5b5=______.-高二数学

题目简介

等差数列{an},{bn}的前n项和分别为An,Bn,且AnBn=7n+45n+3,则a5b5=______.-高二数学

题目详情

等差数列{an},{bn}的前n项和分别为An,Bn,且
An
Bn
=
7n+45
n+3
,则
a5
b5
=______.
题型:填空题难度:中档来源:不详

答案

∵数列{an},{bn}均为等差数列,且其前n项和分别为An,Bn,
a5
b5
=
a1+a9
2
b1+b9
2
=
(a1+a9)•9
2
(b1+b9)•9
2
=
A9
B9

An
Bn
=class="stub"7n+45
n+3

a5
b5
=
A9
B9
=class="stub"7×9+45
9+3
=9

故答案为:9.

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