: 1. C 2n取n-1:C 2n-2取n=132:35 求n值? 2n (2n)(2n-1)(2n-2)! 2n-2 (2n-2)! 35xC = 35x------------------------ = 132xC = 132x---------- n-1 (n+1)(n)!(n-1)(n-2)! n (n-2)!n! (2n)(2n-1) => 35x------------ = 132 => 35(4n^2-2n) = 132(n^2-1) => 140n^2-70n = 132n^2-132 (n+1)(n-1) => 8n^2-70n+132=0 => 4n^2-35n+66=0 => (n-6)(4n-11)=0 => n = 6 : 2. P n+2取4:P 8取n=1:2 n=? 8 n+2 8! (n+2)! 8x7x6x5x4x3 P = 2xP => -------- = 2x-------- = 2(n+2)(n+1)(n)(n-1) => ------------- = (n+2)(n+1)(n)(n-1) n 4 (8-n)! (n-2)! (8-n)! 8x7x6x5x4x3 = (n+2)(n+1)(n)(n-1)(8-n)! 无解?? : 3. 渡船4艘，每艘最多可载5人 : 7人同时过渡，安全过渡的方法数? 有大大在推文中解了~ : 谢谢各位大大，让我问那麽多题而没有嘘我 -- ※ 编辑: hsnuyi (118.168.236.205 台湾), 09/10/2019 17:01:19