摘要: \[ \begin{array} \ 设集合D = \{a, -b\},首项为x.\\ S = x + (x + d_1) + (x + d_1 + d_2) + (x + d_1 + d_2 + d_3) + ... + (x + ... + d_{n-1})\\ \ \ \ = nx + (n 阅读全文
posted @ 2020-09-12 15:27 yys_c 阅读(184) 评论(0) 推荐(0) 编辑