等差数列{an}的前n项和为Sn,若a1≠0,S4=a4,则S8S5=()A.1B.2C.3D.4-数学

题目简介

等差数列{an}的前n项和为Sn,若a1≠0,S4=a4,则S8S5=()A.1B.2C.3D.4-数学

题目详情

等差数列{an}的前n项和为Sn,若a1≠0,S4=a4,则
S8
S5
=(  )
A.1B.2C.3D.4
题型:单选题难度:偏易来源:不详

答案

设等差数列{an}的首项为a1≠0,公差为d,
 由S4=a4,得4a1+6d=a1+3d,得a1=-d≠0,
S8
S5
=
8a1+class="stub"8×7
2
×d
5a1+class="stub"5×4
2
×d
=
8a1+28d
5a1+10d
=class="stub"20d
5d
=4,
故选D.

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