摘要:
\[ \large\begin{aligned} &\sum_{i=0}^n\binom{n}{i}p^i\left \lfloor \frac{i}{k} \right \rfloor \\ =&\sum_{i=0}^n\binom{n}{i}p^i \frac{i-i \bmod k}{k} \ 阅读全文
摘要:
枚举进球个数,得: \[ \large\begin{aligned} &\sum_{i=0}^k \binom{m}{i}\binom{n-m}{k-i} i^l\\ =&\sum_{i=0}^k \binom{m}{i}\binom{n-m}{k-i} \sum_{j=0}^{i} \binom{ 阅读全文