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![[Post New]](/templates/default/images/icon_minipost_new.gif) 2 Apr 2008 22:17:19 IST
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find the sum of products of first n natural numbers taken 2 at a time
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2 Apr 2008 22:30:05 IST
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Do u mean
like
1.2+1.3+1.4+...1.n
+2.3+2.4+2.5..2.n
+...(n-1)n
then is the answer
n2(n+1)2/4-n(n+1)(2n+1)/6?
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" Always remember money isn't everything but make sure you have made a lot of it before talking such nonsense!"
- Bill Gates |
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2 Apr 2008 22:31:19 IST
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wats the answer??
is it n(n+1)(3-2n^2-2n)/48
method
(1+2+3+.....)^2=(1^2+2^2+3^2+......)+2(1.2+2.3+3.4+.........)
1+2+3.....=n(n+1)/2
1^2+2^2+......=n(n+1)(2n+1)/6.........
substituting the values u can get the answer.....
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2 Apr 2008 22:34:30 IST
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thnx
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2 Apr 2008 22:37:03 IST
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akhil, u forgot to divide ans u hv given by 2.....
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2 Apr 2008 22:42:21 IST
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yea thnx
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