Summing a Geometric Series: Can We Use the Formula 1/(1-x)?

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SUMMARY

The discussion centers on the summation of the geometric series \(\sum_{n=0}^{\infty} 2^{-n}\) and its relation to the formula \(\frac{1}{1-x}\). Fred initially suggests that the series can be equated to the formula, but a participant clarifies that this is incorrect as one side represents a numerical value while the other is a power series in \(x\). The correct approach involves recognizing that \(2^{-n}\) can be expressed as \((2^{-1})^n\) and that the series converges under specific conditions.

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  • Understanding of geometric series and convergence criteria
  • Familiarity with the formula for the sum of a geometric series: \(\frac{1}{1-x}\)
  • Knowledge of power series and their properties
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Mathman23
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Hi

Can I claim that in order to find the sum of the series:

\sum_{n = 0} ^{\infty} 2^{- n}

\sum_{n = 0} ^{\infty} 2^{- n} = \sum_{n = 0} ^{\infty} x^n = \frac{1}{1-x} ?


Sincerely Yours
Fred
 
Last edited:
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No, you can't claim *that* (since it is false; one side is a number, the other is a power series in x), but you can use the series if you do so legitimately.
 
In other words, since 2-n= (2-1)n, yes, if x= 2-1. (Assuming, of course, that the sum converges. Can you show that?)
 

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