Sn=(2^2+1)/(2^2-1)+(3^2+1)/(3^2-1)+…+(n^2+1)/(n^2-1)+[(n+1)^
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Sn=(2^2+1)/(2^2-1)+(3^2+1)/(3^2-1)+…+(n^2+1)/(n^2-1)+[(n+1)^2+1]/[(n+1)^2-1]
看通项即可
(n²+1)/(n²-1)
=(n²-1+2)/(n²-1)
=(n²-1)/(n²-1)+2/(n²-1)
=1+2/(n-1)(n+1)
=1+1/(n-1)-1/(n+1)
∴ (2^2+1)/(2^2-1)+(3^2+1)/(3^2-1)+…+(2005^2+1)/(2005^2-1).
=(1+1/1-1/3)+(1+1/2-1/4)+(1+1/3-1/5)+.............+(1+1/2004-1/2006)
=(1+1+1+...........+1)+(1-1/3+1/2-1/4+1/3-1/5+.......+1/2004-1/2006)
2004个
=2004+(1+1/2-1/2005-1/2006)
以下化简即可。
看通项即可
(n²+1)/(n²-1)
=(n²-1+2)/(n²-1)
=(n²-1)/(n²-1)+2/(n²-1)
=1+2/(n-1)(n+1)
=1+1/(n-1)-1/(n+1)
∴ (2^2+1)/(2^2-1)+(3^2+1)/(3^2-1)+…+(2005^2+1)/(2005^2-1).
=(1+1/1-1/3)+(1+1/2-1/4)+(1+1/3-1/5)+.............+(1+1/2004-1/2006)
=(1+1+1+...........+1)+(1-1/3+1/2-1/4+1/3-1/5+.......+1/2004-1/2006)
2004个
=2004+(1+1/2-1/2005-1/2006)
以下化简即可。
![Sn=(2^2+1)/(2^2-1)+(3^2+1)/(3^2-1)+…+(n^2+1)/(n^2-1)+[(n+1)^](/uploads/image/z/19769228-44-8.jpg?t=Sn%3D%282%5E2%2B1%29%2F%282%5E2-1%29%2B%283%5E2%2B1%29%2F%283%5E2-1%EF%BC%89%2B%E2%80%A6%2B%EF%BC%88n%5E2%2B1%29%2F%28n%5E2-1%29%2B%5B%28n%2B1%29%5E)
由最后一项化简整理得:
[﹙n+1﹚²+1]/[﹙n+1﹚²-1]
=[n²+2n+2]/[n﹙n+2﹚]
=[n﹙n+2﹚+2]/[n﹙n+2﹚]
=1+2/[n﹙n+2﹚]
=1+[1/n-1/﹙n+2﹚]
∴以上每一项都可以拆成这种形式:
Sn=[1+﹙1/1-1/3﹚]+[1+﹙1/2-1/4﹚]+[1+﹙1/3-1/5﹚]+[1+﹙1/4-1/6﹚]+……+﹛1+[1/﹙n-1﹚-1/﹙n+1﹚]﹜+﹛1+[1/n-1/﹙n+2﹚]﹜
=1×n+﹛[1+1/2]+[-1/﹙n+1﹚-1/﹙n+2﹚]﹜
=n+n/﹙n+1﹚+n/[2﹙n+2﹚]
[﹙n+1﹚²+1]/[﹙n+1﹚²-1]
=[n²+2n+2]/[n﹙n+2﹚]
=[n﹙n+2﹚+2]/[n﹙n+2﹚]
=1+2/[n﹙n+2﹚]
=1+[1/n-1/﹙n+2﹚]
∴以上每一项都可以拆成这种形式:
Sn=[1+﹙1/1-1/3﹚]+[1+﹙1/2-1/4﹚]+[1+﹙1/3-1/5﹚]+[1+﹙1/4-1/6﹚]+……+﹛1+[1/﹙n-1﹚-1/﹙n+1﹚]﹜+﹛1+[1/n-1/﹙n+2﹚]﹜
=1×n+﹛[1+1/2]+[-1/﹙n+1﹚-1/﹙n+2﹚]﹜
=n+n/﹙n+1﹚+n/[2﹙n+2﹚]
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