2015经济类联考数学数列专题4
1.在等差数列中，已知http://file.koolearn.com/2014/0219/20140219031025195.gif
=21，则
http://file.koolearn.com/2014/0219/20140219031035461.gif
等于( )
(A)132 (B)144 (C) 147 (D)154 (E)128
2.在-12和6之间插入n个数，使这n+2个数组成和为-21的等差数列，则n为
(A)4 (B)5 (C)6 (D)7 (E)8
3.若{
http://file.koolearn.com/2014/0219/20140219031035748.gif
}是等比数列，下面四个命题中
①数列{
http://file.koolearn.com/2014/0219/20140219031035494.gif
}也是等比数列 ②数列{
http://file.koolearn.com/2014/0219/20140219031036331.gif
}也是等比数列
③数列{
http://file.koolearn.com/2014/0219/20140219031036769.gif
}也是等比数列 ④数列{|
http://file.koolearn.com/2014/0219/20140219031035748.gif
|}也是等比数列
正确命题的个数是
(A)1个 (B)2个 (C)3个 (D)4个 (E)5个
4.三个数顺序排列等比数列，其和为114，这三个数依前面的顺序又是某等数列的第1，4，25项，则此三个数的各位上的数字之和为
(A)24 (B)33 (C)24或33 (D)22或33 (E)22
5.如果数列
http://file.koolearn.com/2014/0219/20140219031037578.gif
http://file.koolearn.com/2014/0219/20140219031041996.gif
和数列
http://file.koolearn.com/2014/0219/20140219031048552.gif
http://file.koolearn.com/2014/0219/20140219031041996.gif
都是等差数列，则(
http://file.koolearn.com/2014/0219/20140219031049321.gif
)与(
http://file.koolearn.com/2014/0219/20140219031053586.gif
)的比值为
(A)
http://file.koolearn.com/2014/0219/20140219031058540.gif
(B)
http://file.koolearn.com/2014/0219/20140219031113152.gif
(C)
http://file.koolearn.com/2014/0219/20140219031113402.gif
(D)
http://file.koolearn.com/2014/0219/20140219031114729.gif
(E)以上答案均不正确
答案：1. C 2. B 3. D 4. C 5.C
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