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[单选题]
已知数列-1,a1,a2,-4成等差数列,-1,b1,b2,b3,-4成等比数列,则(a2-a1)/b2的值是()
A.1/2
B.-1/2
C.-1/2 或1/2
D.1/4
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A、1/2
![](https://static.youtibao.com/asksite/comm/h5/images/solist_ts.png)
A.1/2
B.-1/2
C.-1/2 或1/2
D.1/4
A、1/2
已知{an},{bn}分别为等比数列与等差数列,a1=b1=1,则b2≥a2.
(1)a2>0
(2)a10=b10E.
已知等差数列的公差d≠0,a1=1/2,且a1,a2,a5成等比数列.
(I)求{an}的通项公式;
(Ⅱ)若{an}的前n项和Sn=50,求n
请帮忙给出每个问题的正确答案和分析,谢谢!
A.4 005
B.4 006
C.4 007
D.4 008
已知一个等差数列的首项为1,公差为3,那么该数列的前5项和为 ()
A.35
B.30
C.20
D.10
A.=2*$A$1
B.=2*A1
C.=24+$A$1
D.=2+A1