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更新1:
For question 3, the last 2 steps, why the ans is (r+1)!, but not (r!)(r+1)??? Please explain...
重酬!! SUPER EASY MATHS (好趕ga)
2011-01-08 3:21 am
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回答 (2)
2011-01-08 3:35 am
✔ 最佳答案
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2011-01-10 21:25:53 補充：
(r+1)! = (r+1)(r)(r-1)(r-2)...(3)(2)(1)
=(r+1)(r!)
收錄日期: 2021-04-23 23:23:12
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20110107000051KK00921