【497】多重求和
摘要:
$$\begin{equation}\begin{split}\sum_{1 \le j,k \le n} {a_j b_k}& = (\sum_{j=1}^{n} {a_j})(\sum_{k=1}^{n} {b_k})\\\\& = \sum_{j=1}^{n} {a_j (\sum_{k=1} 阅读全文
posted @ 2020-10-27 09:32 McDelfino 阅读(520) 评论(0) 推荐(0)