两等差数列{an}、{bn}的前n项和的比SnS′n=5n+32n+7,a3b3的值是______.-数学

题目简介

两等差数列{an}、{bn}的前n项和的比SnS′n=5n+32n+7,a3b3的值是______.-数学

题目详情

两等差数列{an}、{bn}的前n项和的比
Sn
Sn
=
5n+3
2n+7
a3
b3
的值是______.
题型:填空题难度:中档来源:不详

答案

a3
b3
=
a1+a5
b1+b5
=
class="stub"5
2
(a
1
+a5)
class="stub"5
2
(b
1
+b5)
=
S5
S5
Sn
Sn
=class="stub"5n+3
2n+7

a3
b3
=class="stub"5×5+3
2×5+7
=class="stub"28
17

故答案为:class="stub"28
17

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