更新1:
n!/(n-r+1)(n-r)!= n!/(n-(r-1))! why??
MATH & STAT
回答 (1)
2010-09-07 6:49 am
✔ 最佳答案
n!/(n-r+1)(n-r)!=n!/(n-r+1)!
=[n(n-1)(n-2)....(n-r+2)(n-r+1)!]/(n-r+1)!
=n(n-1)(n-2)....(n-r+2)
2010-09-06 23:40:49 補充：
(n-r+1)(n-r)!=(n-r+1)!=(n-(r-1))!
收錄日期: 2021-04-22 00:51:28
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20100906000051KK01608