1 . 某校为了增强学生的安全意识,组织学生参加安全知识答题竞赛,每位参赛学生可答题若干次,答题赋分方法如下:第一次答题,答对得2分,答错得1分;从第二次答题开始,答对则获得上一次答题得分的两倍,答错得1分.学生甲参加这次答题竞赛,每次答对的概率为
,且每次答题结果互不影响.
(1)求学生甲前三次答题得分之和为4分的概率;
(2)设学生甲第
次答题所得分数
的数学期望为
.
(ⅰ)求
,
,
;
(ⅱ)直接写出
与
满足的等量关系式(不必证明);
(ⅲ)根据(ⅱ)的等量关系求
表达式,并求满足
的
的最小值.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/bf31876698721a199c7c53c6b320aa86.png)
(1)求学生甲前三次答题得分之和为4分的概率;
(2)设学生甲第
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2c05b9832b09731a574d4a4adf7448de.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/bcc33772a68d3e249aab039ab0d3f572.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b53c671e8081b5cc433138e87d5fddd9.png)
(ⅰ)求
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/160d542c7254eb199f89cb76bdc726b7.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/fa7344b7def45826d3ff5939282bbb33.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6468912b3e325881b3caf2d52f030631.png)
(ⅱ)直接写出
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b53c671e8081b5cc433138e87d5fddd9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/00418e8aa72578005947d34081715b8b.png)
(ⅲ)根据(ⅱ)的等量关系求
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b53c671e8081b5cc433138e87d5fddd9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4093d359dfe5f6a23e852773af246561.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2c05b9832b09731a574d4a4adf7448de.png)
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解题方法
2 . 设数轴上有一只兔子,从坐标
开始,每秒以
的概率向正方向跳一个单位,以
的概率向反方向跳一个单位,记兔子第n秒时的位置为
.
(1)证明:
;
(2)记
是表达式
的最大值,证明:
.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/909736dad505d81be43aef91e6309bf4.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/bebfa2855f0e72a3467608ac7999a366.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9e0f663ed52ce99039796233fd7c89c8.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0b15772618afd0ae294ef6860ee60b1d.png)
(1)证明:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c6d840119437cc7897e5041535d46a57.png)
(2)记
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/38fcec7af3520884b173b29bda6c657a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e8f6f251d49337d8a57f740c45e925fe.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/22f7863a1482496025c3205e9b3533f9.png)
您最近一年使用:0次