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#1
24 ¾ÄȨԡÒ¹ 2014, 13:57
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͹ءÃÁ¤ÃѺ
$ \sum_{n = 1}^{\infty}\frac{1}{n(n+1)(n+2)} $
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#2
24 ¾ÄȨԡÒ¹ 2014, 15:02
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$$\frac{1}{2} \sum_{n = 1}^{\infty} \frac{1}{n(n+1)}-\frac{1}{(n+1)(n+2)}$$
$$=\frac{1}{4}$$
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