C (n,r) = n! / r! (n-r)!
在n個( )中每次抽r個b,和 n -r個a
- 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