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[Post New]4 May 2008 21:40:28 IST
    Subject: Re:Find the sum using only calculus
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ramkumar_november (1270)

Blazing goIITian

Olaaa!! Perrrfect answer. 230  [290 rates]
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for the first problem the required sum is.....


S = 1+2x+3x^2+4x^3+.....+nx^{n-1}


now consider


T =  x+x^2+x^3+x^4+....+x^n


using sum of GP formula


T = x+x^2+x^3+x^4+....+x^n  =    \frac{x(x^n-1)}{x-1}


now find \frac{dT}{dx}  which will give you S


 
 this reply: 7 points  (with 1 Olaaa!! Perrrfect answer.   in 2 votes )   [?]
 
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