Math Problem Statement

What are all values of p for which the series \( \sum_{n=1}^{\infty} \frac{1}{n^{2p} + n} \) diverges?

Solution

The series in question is:

n=11n2p+n\sum_{n=1}^{\infty} \frac{1}{n^{2p} + n}

To determine for which values of pp the series diverges, let's first analyze the behavior of the general term.

For large values of nn, the term n2p+nn^{2p} + n behaves approximately as n2pn^{2p}, since the term n2pn^{2p} dominates over nn for large nn. Thus, the general term behaves like:

1n2p\frac{1}{n^{2p}}

Now, we can use the p-series test to determine convergence or divergence. A p-series of the form 1nq\sum \frac{1}{n^q} converges if q>1q > 1 and diverges if q1q \leq 1.

Therefore, we require 2p>12p > 1 for convergence. Solving for pp, we get:

2p>1p>122p > 1 \quad \Rightarrow \quad p > \frac{1}{2}

Hence, the series converges when p>12p > \frac{1}{2} and diverges when p12p \leq \frac{1}{2}.

Conclusion:

The series diverges for p12p \leq \frac{1}{2}, which corresponds to option A.

Let me know if you'd like further explanation or details! Here are some follow-up questions:

  1. How does the comparison test relate to this series?
  2. Can we apply the integral test to this series?
  3. What is the behavior of the series for values of pp much larger than 1/21/2?
  4. How does the term n2p+nn^{2p} + n affect the convergence for small nn?
  5. What other types of series tests could we apply to analyze convergence here?

Tip: For series with terms involving polynomials like this, it's helpful to compare the terms with simpler p-series forms to determine convergence behavior.

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Math Problem Analysis

Mathematical Concepts

Series Convergence
P-Series Test
Asymptotic Analysis

Formulas

P-Series Test: \( \sum \frac{1}{n^q} \) converges if \( q > 1 \)
Approximation: \( n^{2p} + n \approx n^{2p} \) for large \( n \)

Theorems

P-Series Convergence Theorem

Suitable Grade Level

Undergraduate Mathematics