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变通公式巧妙解题２５１７００山东惠民县一中吴庆余等差数列（ａｎ）：ａｎ＝ａ１十（ｎ－１）ｄ公式可巧妙地将ａｎ与Ｓｎ转换，用此公式处理ａｎ与Ｓｎ关系思路清新，功效独到．例１等差数列ａｎ前ｎ项和Ｓ。一５；ｌ’＋３ｎ求通项ａ。（例２在等差数列｛ａ。｝中，前...
Inflexible Formula Solving Problem 251700 Shandong Huimin County Yizhong Wu Qingyu Arithmetic Series (an):an=a1 The ten (n-1)d formula can be used to convert an and Sn skillfully. Use this formula to deal with the relationship between an and Sn. , unique effect. Example 1 The arithmetic series an before n and S. One 5; l’+3n finds term a. (Example 2 in the arithmetic sequence {a.}, before...