![](https://static.youtibao.com/asksite/comm/h5/images/m_q_title.png)
[单选题]
已知等差数列{an}中,a3+a5=a4+7,a10=19,则数列{ancos nπ}的前2 018项和为()
A.1 008
B.1 009
C.2 017
D.2 018
![](https://static.youtibao.com/asksite/comm/h5/images/m_q_a.png)
D、2 018
![](https://static.youtibao.com/asksite/comm/h5/images/solist_ts.png)
A.1 008
B.1 009
C.2 017
D.2 018
D、2 018
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
已知数列{an}是等比数列,且a>0,a2a4+2a3a5+a4a6=25,那么a3+a5的值等于
A.5
B.10
C.15
D.20
等差数列{an}的公差d<0,且a2·a4=12,a2+a4=8,则数列{an}的通项公式是()
A.an=2n-2
B.an=2n+4
C.an=-2n+12
D.an=-2n+10
等差数列{an)中,已知a5+a8=5,那么a2+a11的值等于 ()
A.5
B.10
C.15
D.20