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Math Help - Question about Series convergance

  1. #1
    Member moonnightingale's Avatar
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    Question about Series convergance

    My book has writen this. Series is attached


    How he has converged the series
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  2. #2
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    That's almost a geometric series. There is a general formula that
    \sum_{n=0}^\infty ar^n= \frac{a}{1- r}.

    Now, the derivative, term by term, is \sum_{n=0}^\infty a_n r^{n-1} and that must be equal to the derivative, with respect to r, of \frac{a}{1- r}.
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  3. #3
    Member moonnightingale's Avatar
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    Why book has used (Square) in denominator???
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