Ok so when differentiating(adsbygoogle = window.adsbygoogle || []).push({});

1/(1-x)= Σ x^{n}from n=0 to infinity

the book says it is 1/(1-x)^2 = Σ n*(x)^{n-1}from n=1 to infinity

i dont understand why the original sum starts at 0 and then the derived sum starts at 1

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# I Question about the derivative of this sum and where n starts

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