Math Problem Statement

convergent or divergent

Is the series \( \frac{x}{1+x} - \frac{x^2}{1+x^2} + \frac{x^3}{1+x^3} - \cdots \) convergent or divergent, where \(0 < x < 1\)?

Solution

The given series is:

x1+xx21+x2+x31+x3\frac{x}{1+x} - \frac{x^2}{1+x^2} + \frac{x^3}{1+x^3} - \cdots

where 0<x<10 < x < 1.

To determine if this series is convergent or divergent, let's analyze the behavior of the terms.

  1. Observing Terms: Each term of the series is of the form xn1+xn\frac{x^n}{1 + x^n}, and the terms alternate in sign. For 0<x<10 < x < 1, as nn becomes large, xnx^n approaches 0 because xx is a fraction, which causes each term xn1+xn\frac{x^n}{1 + x^n} to approach 0.

  2. Convergence Criteria: Since this series has alternating terms and the absolute value of each term xn1+xn\frac{x^n}{1 + x^n} tends toward 0, we can apply the Alternating Series Test (also known as the Leibniz criterion) for convergence:

    • The terms decrease in magnitude as nn increases.
    • The limit of each term as nn \to \infty is 0.

    Both conditions are satisfied.

  3. Conclusion: By the Alternating Series Test, the series is convergent.

Would you like a more detailed breakdown of each step?

Here are some related questions for deeper exploration:

  1. How does the Alternating Series Test work, and why does it imply convergence?
  2. What happens if xx is close to 1? Does it impact the convergence rate?
  3. Can we find the sum of this series for specific values of xx?
  4. Is there an alternative test that could confirm convergence for this series?
  5. How would the convergence behavior change if the terms did not alternate in sign?

Tip: In alternating series, if the terms decrease in magnitude to zero, it’s generally convergent by the Alternating Series Test.

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Math Problem Analysis

Mathematical Concepts

Series Convergence
Alternating Series

Formulas

\( \frac{x^n}{1 + x^n} \) for each term in the series

Theorems

Alternating Series Test (Leibniz Criterion)

Suitable Grade Level

Undergraduate Mathematics