一列數(shù)a
1,a
2,a
3,…,其中a
1=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101193730265314617/SYS201311011937302653146010_ST/0.png)
,a
n=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101193730265314617/SYS201311011937302653146010_ST/1.png)
(n為不小于2的整數(shù)),則a
4的值為( )
A.
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101193730265314617/SYS201311011937302653146010_ST/2.png)
B.
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101193730265314617/SYS201311011937302653146010_ST/3.png)
C.
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101193730265314617/SYS201311011937302653146010_ST/4.png)
D.
【答案】
分析:將a
1=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101193730265314617/SYS201311011937302653146010_DA/0.png)
代入a
n=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101193730265314617/SYS201311011937302653146010_DA/1.png)
得到a
2的值,將a
2的值代入,a
n=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101193730265314617/SYS201311011937302653146010_DA/2.png)
得到a
3的值,將a
3的值代入,a
n=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101193730265314617/SYS201311011937302653146010_DA/3.png)
得到a
4的值.
解答:解:將a
1=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101193730265314617/SYS201311011937302653146010_DA/4.png)
代入a
n=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101193730265314617/SYS201311011937302653146010_DA/5.png)
得到a
2=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101193730265314617/SYS201311011937302653146010_DA/6.png)
=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101193730265314617/SYS201311011937302653146010_DA/7.png)
,
將a
2=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101193730265314617/SYS201311011937302653146010_DA/8.png)
代入a
n=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101193730265314617/SYS201311011937302653146010_DA/9.png)
得到a
3=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101193730265314617/SYS201311011937302653146010_DA/10.png)
=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101193730265314617/SYS201311011937302653146010_DA/11.png)
,
將a
3=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101193730265314617/SYS201311011937302653146010_DA/12.png)
代入a
n=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101193730265314617/SYS201311011937302653146010_DA/13.png)
得到a
4=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101193730265314617/SYS201311011937302653146010_DA/14.png)
=
![](http://thumb.zyjl.cn/pic6/res/czsx/web/STSource/20131101193730265314617/SYS201311011937302653146010_DA/15.png)
.
故選A.
點評:本題考查了數(shù)列的變化規(guī)律,重點強調(diào)了后項與前項的關(guān)系,能理解通項公式并根據(jù)通項公式算出具體數(shù).
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