Finding Radius of Convergence: Ratio Test for Series

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SUMMARY

The discussion focuses on determining the interval of convergence for the series \(\sum \frac{(2k+1)!}{(2k)(k!)^2} x^k\) using the Ratio Test. The user successfully identified the interval as \((-1/2, 1/2)\) but encountered difficulties assessing the convergence at the endpoints. The Ratio Test yielded a limit of 1 at \(x = -1/2\), indicating that the test is inconclusive. The user is advised to apply the Endpoint Test to further analyze convergence at the boundaries.

PREREQUISITES
  • Understanding of power series and their convergence properties.
  • Familiarity with the Ratio Test for series convergence.
  • Knowledge of endpoint convergence tests, such as the Direct Comparison Test or the Alternating Series Test.
  • Basic factorial manipulation and properties of limits.
NEXT STEPS
  • Learn about the Direct Comparison Test for series convergence.
  • Study the Alternating Series Test and its application to endpoint analysis.
  • Explore the concept of absolute convergence and its implications for series.
  • Review advanced techniques for determining convergence of power series.
USEFUL FOR

Students studying calculus, particularly those focusing on series and convergence tests, as well as educators seeking to clarify concepts related to power series and convergence criteria.

Fiz2007
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Homework Statement


find the interval of convergence of
[tex]\sum[/tex][(2k+1)!/((2k)((k!)2)]* [xk]


Homework Equations


Ratio Test


The Attempt at a Solution


I already found that it converges on (-1/2, 1/2) by using power series with b=0 and testing the rest of it as ak. However, I am unsure about the end points. I tried using the ratio test with x = (-1/2) and I get the limit to be 1 so the test fails. What test would I be able to use? Any help is greatly appreciated.
 
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And i have no clue why the summation is putting all the stuff in there but it is suppose to say just what is in the text at the end.
 
A series can't converge if the limit of the terms doesn't go to zero. Try that test at the endpoints.
 

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