名校
解题方法
1 . 设
,
,甲、乙、丙三个口袋中分别装有
、
、
个小球,现从甲、乙、丙三个口袋中分别取球,一共取出
个球.记从甲口袋中取出的小球个数为
.
(1)当
时,求
的分布列;
(2)证明:
;
(3)根据第(2)问中的恒等式,证明:
.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0704f453b2de48d36911f7db496bbf82.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e145b6046bc80d0ffecc61ac67c87ca1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5aadf9ab510510120699c5eee39ab18b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7a0876215b2fd463d151523cd3c6b447.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f022950e0faa45b617d497b01b5292b9.png)
(1)当
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e45cf86650443d1b86c79b1e3edc7e5c.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f022950e0faa45b617d497b01b5292b9.png)
(2)证明:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/55f9644be56c2e615ec39756edaebcdb.png)
(3)根据第(2)问中的恒等式,证明:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5236de8376cdab17922e71bc14fb875e.png)
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