Is There an Analytical Solution for This Mathematical Series?

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Discussion Overview

The discussion revolves around the possibility of finding an analytical solution for a mathematical series expressed as \(\sum_{k=1}^t a^{t-k}b^{k-1}\). Participants explore the nature of the series, its representation as a polynomial, and methods for calculating it.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant questions whether an analytical result can be obtained for the series.
  • Another participant asserts that the expression is a polynomial in two variables rather than a series.
  • A participant acknowledges the correction and seeks methods to deal with the polynomial.
  • Suggestions are made to write out terms in the sum to identify familiar patterns.
  • A participant proposes a transformation of the series into a different form, suggesting a potential method for calculation.
  • Another participant provides a specific formula for the sum when \(t\) is uneven, indicating a possible solution.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the nature of the original expression, with some viewing it as a series and others as a polynomial. Multiple approaches to calculating the expression are presented, but no definitive agreement on a single method is established.

Contextual Notes

The discussion includes various interpretations of the expression, and assumptions regarding the conditions under which the proposed formulas apply remain unresolved.

phonic
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Is it possible to get a analytical result for this series? It looks simple:

[itex]\sum_{k=1} ^t a^{t-k}b^{k-1}[/itex]

Thanks a lot!
 
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Hmm.Use [ tex ] & [ /tex ] commands (without the spaces) for opening & closing tex tags.

That's no series,it's a polynomial in 2 variables.

Daniel.
 
Thanks for your corection. It's my first time to post message here.

Yes, this is a polynomial, with all coeficient as 1. Is there some method to deal with it?
 
Yes,try to write some terms in the sum and then see whether you recognize something familiar.

Daniel.
 
Thanks for your hints. I think it can be calculated in this way:
[tex]\sum_{k=1} ^t a^{t-k}b^{k-1} = \frac{a^t}{b}\sum_{k=1} ^t (\frac{b}{a})^{k}[/tex]
 
It's easier this way:

[tex]\sum_{k=1}^{t} a^{t-k}b^{k-1}=a^{t-1}b^{0}+a^{t-2}b^{1}+...+a^{1}b^{t-2}+a^{0}b^{t-1}=\frac{a^{t}-b^{t}}{a-b}[/tex]

with "t" uneven.

Daniel.
 

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