![](https://static.youtibao.com/asksite/comm/h5/images/m_q_title.png)
[单选题]
已知数列{an}的前n项和Sn=3n,则a5+a6+a7+a8等于()
A.8
B.12
C.14
D.19
![](https://static.youtibao.com/asksite/comm/h5/images/m_q_a.png)
B、12
![](https://static.youtibao.com/asksite/comm/h5/images/solist_ts.png)
A.8
B.12
C.14
D.19
B、12
已知数列{an}的前n项和为Sn,且S2n-1=4n2-2n+1,则Sn等于() (A)n2+n (B)n2+n+1 (C)4n2+l (D)4n2-2n
已知数列{an}的前n项和Sn=n(2n+1)
(I)求该数列的通项公式;
(Ⅱ)判断39是该数列的第几项
已知等比数列{an}中,a1=16,公比q=(1/2)
(Ⅰ)求数列{an}的通项公式;
(Ⅱ)若数列{an}的前n项的和Sn=124,求n的值
已知等差数列{an}的前n项和为Sn,若a4=18-a5,则S8等于
A.18
B.36
C.54
D.72
等差数列{an}的前n项和为Sn,已知S3=3,S6=24,则此等差数列的公差d等于().
A.3
B.2
C.1
D.
E.