Binomial series (radius of convergence)

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SUMMARY

The radius of convergence for binomial series is not universally 1. The binomial series defined as $\displaystyle\sum_{k=0}^{\infty} \; {\alpha \choose k} \; x^k$ converges absolutely to $(1+x)^{\alpha}$ for all $\alpha \in \mathbb{R}$ when $|x| < 1$. However, if $\alpha$ is a non-negative integer, the series becomes finite, resulting in a radius of convergence of $+\infty$. This distinction is crucial for understanding the behavior of binomial series across different values of $\alpha$.

PREREQUISITES
  • Understanding of binomial coefficients, denoted as ${\alpha \choose k}$
  • Knowledge of series convergence criteria
  • Familiarity with the concept of radius of convergence
  • Basic grasp of real numbers and their properties
NEXT STEPS
  • Study the convergence of power series in detail
  • Explore the properties of binomial coefficients and their applications
  • Learn about the implications of different values of $\alpha$ on series convergence
  • Investigate other series with varying radii of convergence
USEFUL FOR

Mathematicians, students studying calculus or real analysis, and anyone interested in the properties of series and convergence in mathematical contexts.

Fernando Revilla
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I quote a question from Yahoo! Answers

Is the radius of convergence for all binomial series exactly 1?

I have given a link to the topic there so the OP can see my response.
 
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If $|x|<1$, the binomial series $\displaystyle\sum_{k=0}^{\infty} \; {\alpha \choose k} \; x^k $ converges absolutely to $(1+x)^{\alpha}$ for any $\alpha\in\mathbb{R}$, but not always the radius of convergence is $1$. For example, if $\alpha$ is a non-negative integer, then the series is finite and the radius of convergence is $+\infty$.
 

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