7楼: Originally posted by jabile at 2015-03-26 10:20:00
A_1\cup A_2 \cup \cdots \cup A_n|\\
=\sum_{k=1}^n (-1)^{k+1} \\
=\sum_{k=1}^n (-1)^{k+1} \\
=\sum_{k=1}^n (-1)^{k+1} {n!\over k!}\\
=n!...

11楼: Originally posted by Jeydragon at 2015-03-28 20:47:57
非常非常非常感谢你的热心和耐心，我只是好奇的是通过大学学习的排列组合或者条件概率之类搞不定吗？这个公式，理解起来总感觉有些困难。...