Bit confused about the geometric series

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SUMMARY

The discussion centers on the sum of a geometric series, specifically the formula \(\sum ar^{n-1} = \frac{a}{1-r}\) for \(|r|<1\). Participants clarify that the starting point of the series significantly impacts the sum, particularly when comparing sums starting at \(n=1\) versus \(n=2\). The correct application of the formula is confirmed as \(\frac{1/4}{1-(1/4)}\) for the series \(\sum (1/4)^{n-1}\) when \(n=1\) to infinity, leading to a sum of \(\frac{4}{3}\). The importance of clearly defined limits in summation notation is emphasized throughout the conversation.

PREREQUISITES
  • Understanding of geometric series and their properties
  • Familiarity with summation notation and limits
  • Basic algebraic manipulation skills
  • Knowledge of convergence criteria for series
NEXT STEPS
  • Study the derivation of the geometric series sum formula
  • Learn about convergence and divergence of series
  • Explore examples of geometric series with varying starting points
  • Investigate the implications of different values of \(r\) in geometric series
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Students and educators in mathematics, particularly those focusing on series and sequences, as well as anyone seeking to clarify the application of geometric series in problem-solving contexts.

  • #31
(just got up :zzz: …)

Bazzinga, you need to learn these two formulas …

for all n:
1 - xn = (1 - x)(1 + x + x2 + … + xn-1)​

for odd n:
1 + xn = (1 + x)(1 - x + x2 - … + xn-1) :wink:
 

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