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MathGroup Archive 2001

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RE: Summation without Mathematica

  • To: mathgroup at
  • Subject: [mg27449] RE: [mg27416] Summation without Mathematica
  • From: "David Park" <djmp at>
  • Date: Sun, 25 Feb 2001 20:55:55 -0500 (EST)
  • Sender: owner-wri-mathgroup at

Sum[x^3*a^x, {x, 1, Infinity}]
% /. a -> 7/8
(a + 4*a^2 + a^3)/(-1 + a)^4

David Park
djmp at 

> From: mrtommorris [mailto:mor3752 at]
To: mathgroup at
> Can someone help me to evaluate the sum from x=1 to infinity for the
> expression x^3(7/8)^x. I know the formulas that will evaluate 
> either alone.
> But the product is giving me difficulty.

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