Find out where this power series converges

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SUMMARY

The discussion focuses on determining the convergence of the power series Ʃ(xn2n) / (3n + n3) using the ratio test. The user applies the ratio test and derives the limit expression pn = 2x (3n + n3)/[(3)(3)n+n3(1+1/n)3]. They conclude that since 3^n grows faster than n^3, the limit approaches |x| < 3/2. The user expresses uncertainty about the behavior at the boundaries and suggests employing l'Hôpital's rule for further analysis.

PREREQUISITES
  • Understanding of power series and convergence criteria
  • Familiarity with the ratio test for series convergence
  • Knowledge of l'Hôpital's rule for limit evaluation
  • Basic algebraic manipulation skills for simplifying expressions
NEXT STEPS
  • Study the application of the ratio test in depth
  • Learn about boundary behavior in power series convergence
  • Explore l'Hôpital's rule with practical examples
  • Investigate other convergence tests such as the root test
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Mathematics students, educators, and anyone studying series convergence in calculus or advanced mathematics courses.

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Homework Statement


Find out where this power series converges.

Ʃ(xn2n) / (3n + n3)


Homework Equations





The Attempt at a Solution



I'm trying to use the ratio test to solve it. I end up with the following equation, which I am unable to reduce further:

pn = 2x (3n + n3)/[(3)(3)n+n3(1+1/n)3]
 
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My guess is, since [itex]3^n[/itex] goes to infinity faster than [itex]n^3[/itex] (exponentials are faster than polynomials), is that your ratios go to [itex]\frac{2}{3}x[/itex]. Tnen you want [itex]|x|<\frac{3}{2}[/itex]. Not sure what happens at the boundaries. To check the limit I guessed at, maybe use l'Hopital's rule 3 times?
 

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