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1 . 富比尼原理又称算两次原理,是组合数学中非常重要的计算方法,下面的组合恒等式可以用富比尼原理进行证明,具体如下:
人中有1人是军人,从
人中选
人各奖励1颗星,共有
种选法,另一方面,这等价于考虑这
人中的军人是否被选中,若选中军人,则有
种选法,若未选中军人,则有
种选法,所以
;
(1)若
,求关于
的方程
的解;
(2)将题干中的问题推广到
人中有
人是军人的情形,写出结论并加以证明.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d2c95df1e638ebfe52ab35c93d4e424c.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7707aba7b9fed2c8e4704b82ce09087a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7b1dac9ce7c08de49a30f1d982bbedee.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/894e4655d43814eae5e21ca44840d918.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4746217439e9cbcfe130bc074736e86b.png)
(1)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f6b54fdc920fd0a627959bbc5bd292d3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/81dea63b8ce3e51adf66cf7b9982a248.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/875978e3eeb54751d2ce83ae18421657.png)
(2)将题干中的问题推广到
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0b367cda0011d8968cb46206aa0bb4aa.png)
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