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[数列] 数列

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lrh2006 posted 2017-6-4 11:07 |Read mode

请各位指点下，怎么做比较好，为什么可以把Sn看成n2?谢谢！ QQ图片20170604110452.png

QQ图片20170604110452.png

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力工 posted 2017-6-4 15:30

回复 1# lrh2006

直接用和的性质：等比，和为关于$q^n$的二项形式，那个什么系数与常数项和为$0$.就成关于$n$的恒等式了。

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original poster lrh2006 posted 2017-6-6 10:06

回复 2# 力工

好的，谢谢

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