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How to find the sum of this infinite series
How can I calculate result of $\sum\limits_{i=1}^n\cfrac{n}{2^n}$ ?
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3$\begingroup$ similar question math.stackexchange.com/questions/50919/… $\endgroup$– AndrewOct 4, 2011 at 17:51
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2$\begingroup$ In the same vein as the two questions cited above:$$\sum_{n=1}^\infty n x^n=\frac{x}{(1-x)^2}$$ $\endgroup$– robjohn ♦Oct 4, 2011 at 18:06
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2$\begingroup$ In above links the upper limit is infinity.But here is n. $\endgroup$– user16948Oct 4, 2011 at 18:19
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$\begingroup$ And the index of summation is $i$. This is somewhat confusing... $\endgroup$– user940Oct 4, 2011 at 19:03
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