Posted by haifeng on 2025-09-09 08:40:10 last update 2025-09-09 08:40:10 | Answers (1) | 收藏
证明: 对任意 $n\geqslant 1$, 有
\[\sum_{k=n+1}^{2n}\frac{1}{k}=\sum_{k=1}^{2n}\frac{(-1)^{k+1}}{k}.\]
