高考数学数列大题训练
已知等比数列
分别是某等差数列的第5项、第3项、第2项,且
(Ⅰ)求
;(Ⅱ)设
,求数列
2.已知数列
满足递推式
,其中
(Ⅰ)求
;
(Ⅱ)求数列
的通项公式;
(Ⅲ)求数列
的前n项和
3.已知数列
的前
项和为
,且有
,
EMBED Equation.DSMT4
(1)求数列
的通项公式;
(2)若
,求数列
的前
项的和
。
4.已知数列{
}满足
,且
.
(Ⅰ)求
,
;(Ⅱ)证明数列{
}是等差数列;
(Ⅲ)求数列{
}的前
项之和
5.已知数列
满足
,
.
(1)求
,
,
;
(2)求证:数列
是等差数列,并写出
的一个通项。
6.数列
的前
项和为
,
,
HYPERLINK "http://wxc.833200.com"
(Ⅰ)求数列
的通项
;
(Ⅱ)求数列
的前
项和
7.
. 求证:
⑴数列{bn+2}是公比为2的等比数列;
⑵
EMBED Equation.3 ;
⑶
EMBED Equation.3 .
8.已知各项都不相等的等差数列
的前六项和为60,且
的等比中项.
(1)求数列
的通项公式
;
(2)若数列
的前n项和Tn.
9.已知
是数列
的前
项和,
,且
,其中
.
求证数列
是等比数列;
求数列
的前
项和
.
10.已知
是数列{
}的前n项和,并且
=1,对任意正整数n,
;设
).
(I)证明数列
是等比数列,并求
的通项公式;
(II)设
的前n项和,求
.
高考数列大题参考
答案
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1.解析:
设该等差数列为
,则
,
,
EMBED Equation.DSMT4
EMBED Equation.DSMT4
EMBED Equation.DSMT4 即:
EMBED Equation.DSMT4 ,
EMBED Equation.DSMT4 ,
EMBED Equation.DSMT4 ,
EMBED Equation.DSMT4
EMBED Equation.DSMT4 ,
的前
项和
当
时,
,
EMBED Equation.DSMT4 (8分)
当
时,
,
EMBED Equation.DSMT4
EMBED Equation.DSMT4
2.解:(1)由
知
解得:
同理得
(2)由
知
EMBED Equation.3 构成以
为首项以2为公比的等比数列;
;
为所求通项公式
(3)
EMBED Equation.3
3.解:由
,
,又
,
,
是以2为首项,
为公比的等比数列,
,
(1)
(2)
(1)—(2)得
即:
,
4.解:(Ⅰ)
,
.
(Ⅱ)
,
∴
, 即
.
∴数列
是首项为
,公差为
的等差数列.
(Ⅲ)由(Ⅱ)得
∴
.
EMBED Equation.3
EMBED Equation.3 . ∴
.
5.解: (1)
(2)证明:由题设可知
是以
为首项,
为公差的等差数列
故
6.解:(Ⅰ)
,
,
HYPERLINK "http://wxc.833200.com"
又
,
数列
是首项为
,公比为
的等比数列,
HYPERLINK "http://wxc.833200.com"
当
时,
,
(Ⅱ)
,
当
时,
;
当
时,
,…………①
,………………………②
得:
EMBED Equation.DSMT4
HYPERLINK "http://wxc.833200.com"
HYPERLINK "http://wxc.833200.com" 又
也满足上式,
7.解: ⑴
数列{bn+2}是首项为4公比为2的等比数列;
⑵由⑴知
……
上列(n-1)式子累加:
⑶
EMBED Equation.3 .
8.解:(1)设等差数列
的公差为
,则
解得
.
(2)由
EMBED Equation.3
9.解:①
EMBED Equation.DSMT4
EMBED Equation.DSMT4
EMBED Equation.DSMT4
EMBED Equation.DSMT4
又
也满足上式,
EMBED Equation.DSMT4
EMBED Equation.DSMT4 (
)
数列
是公比为2,首项为
的等比数列
(2)由①,
EMBED Equation.DSMT4
于是
EMBED Equation.DSMT4
EMBED Equation.DSMT4
10.解析:(I)
两式相减:
是以2为公比的等比数列,
EMBED Equation.3
(II)
EMBED Equation.3
而
EMBED Equation.3
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