Math Problem Statement

Analyze the convergence of the infinite series \( \sum_{n=1}^\infty \frac{2+n}{1-3n} \).

Solution

This is an infinite series given by:

n=12+n13n.\sum_{n=1}^\infty \frac{2 + n}{1 - 3n}.

Steps to Solve or Analyze Convergence

  1. General Form: The term of the series is: an=2+n13n.a_n = \frac{2 + n}{1 - 3n}.

  2. Check Convergence:

    • To determine convergence, analyze the behavior of the term ana_n as nn \to \infty. Specifically, if an↛0a_n \not\to 0, the series diverges.
    • The dominant term in the numerator is nn, and in the denominator, it is 3n-3n. So, limnan=limn2+n13n=limnn3n=13.\lim_{n \to \infty} a_n = \lim_{n \to \infty} \frac{2 + n}{1 - 3n} = \lim_{n \to \infty} \frac{n}{-3n} = \frac{-1}{3}.

    Since an130a_n \to -\frac{1}{3} \neq 0, the series diverges.

Conclusion

The infinite series n=12+n13n\sum_{n=1}^\infty \frac{2 + n}{1 - 3n} diverges because the terms of the sequence do not approach zero.

Would you like further details on series convergence, or do you have additional questions?


Related Questions

  1. What are the criteria for a series to converge or diverge?
  2. How does the divergence test work for infinite series?
  3. Can this series be rearranged or modified to make it converge?
  4. What happens if we consider a partial sum of this series?
  5. How do we deal with series that contain alternating terms?

Tip: Always verify the limit of ana_n before proceeding to more advanced convergence tests.

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Math Problem Analysis

Mathematical Concepts

Infinite Series
Convergence and Divergence
Limit Analysis

Formulas

General term of the series: \( a_n = \frac{2+n}{1-3n} \)
Limit of a sequence: \( \lim_{n \to \infty} a_n \)

Theorems

Divergence Test: If \( \lim_{n \to \infty} a_n \neq 0 \), the series \( \sum a_n \) diverges.

Suitable Grade Level

Undergraduate Math (Calculus Level)