2015经济类联考数学数列专题5
1.数列3，12，30，60，…的一个通项公式是( )(A)
http://file.koolearn.com/2014/0219/20140219031250617.gif
(B)
http://file.koolearn.com/2014/0219/20140219031251402.gif
(C)
http://file.koolearn.com/2014/0219/20140219031251552.gif
(D)
http://file.koolearn.com/2014/0219/20140219031252501.gif
(E)以上答案均不正确
2.若数列{
http://file.koolearn.com/2014/0219/20140219031252512.gif
}的前
http://file.koolearn.com/2014/0219/20140219031255365.gif
项和
http://file.koolearn.com/2014/0219/20140219031256462.gif
，则它的通项公式是( )
(A)
http://file.koolearn.com/2014/0219/20140219031304243.gif
(B)
http://file.koolearn.com/2014/0219/20140219031319121.gif
(C)
http://file.koolearn.com/2014/0219/20140219031320554.gif
(D)
http://file.koolearn.com/2014/0219/20140219031320246.gif
(E)以上答案均不正确
3.已知{an}是等差数列，
http://file.koolearn.com/2014/0219/20140219031320197.gif
，
http://file.koolearn.com/2014/0219/20140219031321351.gif
，则
http://file.koolearn.com/2014/0219/20140219031321142.gif
等于()
(A)30 (B)27 (C)24 (D)21 (E)20
4.在等比数列{
http://file.koolearn.com/2014/0219/20140219031322501.gif
}中，已知Sn=36，S2n=54，则S3n等于
(A)63 (B)68 (C)76 (D)89 (E)86
答案：1. C 2. C 3. B 4. A
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