作者mqazz1 (无法显示)
看板Math
标题[离散] 排容
时间Sat Apr 2 20:32:52 2011
find the number of solutions to the equation
x1 + x2 + x3 + x4 = 18
in which each xi, 1 <= xi <= 9
justify your answer is required
(hint: consider the inclusion and exclusion principle)
谢谢
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1F：推 privatewind :算出全部的 再去掉当一个大於10 两个大於10 ... 04/02 22:49
2F：→ privatewind :这是用他hint 去解，如果不想就用生成函数 04/02 22:49