三行搞定错位相减法

学生初次接触错位相减法是推导等比数列前n项和公式，进而衍生出等差数列乘以等比数列｛ａｎ·ｂｎ｝形式的前ｎ项的和Ｓｎ的方法.在实际教学中学生普遍反应一听就懂，一算纠错.今天介绍一种方法能迅速计算出错位相减法结果的方法.

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你算的每一道错位相减法，其实都是推导一遍下面的公式，如果你非要说锻炼计算能力，那么每次直接练习下方的推导过程即可.

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关于差比数列求和，除常规的错位相减法，还可以利用裂项相消法求得结果，个人不推荐该方法，使用裂项的方法也容易算错.

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原创编写，搬运请带上下图，本文电子版，可尝试在下方微信群下载。