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# 二項式Binomial Expression

C (n,r) = n! / r! (n-r)!

由n個元素中每次抽出r個元素組合

or把他當作在(a+b) *n

在n個( )中每次抽r個b,和 n -r個a

咁仲有在咩時候會用到呢條公式呀?

謝謝呀

### 1 Answer

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- 良師益友Lv 71 decade agoFavorite Answer
Basically both of your statements are correct.

The fundamental definition of nCr is the number of ways you can select r out of n objects random without considering the order of placement, which is equivalent to your first statement.

On the other hand, nCr is also used to denote the coefficient of the rth term in the expansion of ( a + b )^n, which is identical to your second statement.

This nCr relates to Combination which can be seen frequently in the recent Probability questions and also those problems related to Bayes Theorem that appears in M1.

Hope I can help you.

Source(s): Mathematics Teacher Mr. Ip

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