F5 Permutation
2011-04-17 10:59 pm
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回答 (1)
2011-04-17 11:27 pm
✔ 最佳答案
1 P(n,r)= n(n - 1)...(n - r + 1)= (n - r + 1)*n(n - 1)...(n - (r - 1) + 1)= (n - r + 1)P(n,r - 1)2 P(n - 1,r) + rP(n - 1,r-1)= (n - 1)...(n - 1 - r + 1) + r(n - 1)(n - 2)...(n - 1 - r + 1 + 1)= (n - 1)...(n - r) + r(n - 1)(n - 2)...(n - r + 1)= (n - 1)(n - 2)...(n - r + 1)(n - r + r)= n(n - 1)(n - 2)...(n - r + 1)= P(n,r)
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原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20110417000051KK00586