[問題] 兩題離散

看板Grad-ProbAsk作者 (open)時間17年前 (2009/03/16 22:21), 編輯推噓2(2推 0噓 3→)
留言5則, 2人參與, 最新討論串1/1
(a)In how many ways can 3n letters be selected from 2n A's, 2n B's, and 2n C's ? (b)In how many ways can n letters be selected from an unlimited supply of A's , B's ,and C's if each selection must include an even number of A's ? -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 140.114.216.145
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03/16 23:18, , 1F
(a) C(3n+2,2) - 3C(n,1) (b)求1/(1-x^2)(1-x)^2中x^n的係數
03/16 23:18, 1F
推
03/17 00:57, , 2F
請問一下A是怎麼導的???
03/17 00:57, 2F
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03/17 05:02, , 3F
相當於a+b+c=3n，0≦a、b、c≦2n，用排容
03/17 05:02, 3F
推
03/17 19:21, , 4F
喔! 謝嚕!
03/17 19:21, 4F
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03/18 11:32, , 5F
應該是 C(3n+2,2) - 3C(n+1,2) 才對
03/18 11:32, 5F
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