设等差数列{an}的前n项和为Sn,若S9=81,则a2+a5+a8=( ) A.26 B.27 C.28 D.29
设等差数列{an}的前n项和为Sn,若S9=81,则a2+a5+a8=( )
A. 26
B. 27
C. 28
D. 29
数学人气:690 ℃时间:2020-03-12 07:26:20
优质解答
由S
9=
=9a
5=81,得到a
5=9,
则a
2+a
5+a
8=(a
2+a
8)+a
5=3a
5=27.
故选B
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