Math Problem Statement

test for convergence or divergence

Test for convergence or divergence of the series: (2^p / 1^q) + (3^p / 2^q) + (4^p / 3^q) + ... ∞ where p and q are positive numbers.

Solution

The given series is:

n=1npnq=n=1npq\sum_{n=1}^{\infty} \frac{n^p}{n^q} = \sum_{n=1}^{\infty} n^{p-q}

where pp and qq are positive numbers.

Step 1: Simplifying the Series

The general term of the series simplifies to:

npqn^{p-q}

So the series becomes:

n=1npq\sum_{n=1}^{\infty} n^{p-q}

Step 2: Applying the p-series Test

This series resembles a p-series, which is of the form:

n=11nr\sum_{n=1}^{\infty} \frac{1}{n^r}

for some value of rr. In our case, the term is npq=n(qp)n^{p-q} = n^{-(q-p)}. Thus, we can compare this to a p-series with exponent (qp)-(q-p).

The p-series convergence criterion states:

  • If r>1r > 1, the series converges.
  • If r1r \leq 1, the series diverges.

Step 3: Testing Convergence

For our series to converge, we need the exponent qp>1q - p > 1, meaning that q>p+1q > p + 1. If this condition holds, the series converges. Otherwise, the series diverges.

Conclusion:

  • If q>p+1q > p + 1, the series converges.
  • If qp+1q \leq p + 1, the series diverges.

Would you like a deeper explanation on any step? Here are five related questions to consider:

  1. How does the p-series test work for other series forms?
  2. Can this series be tested using the ratio test for more complex cases?
  3. What happens if p=qp = q or p>qp > q?
  4. How would the behavior of the series change if we altered the powers of nn?
  5. Can we express the sum of the series in closed form for specific values of pp and qq?

Tip: Understanding convergence tests (like p-series and ratio tests) is essential for working with infinite series.

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Math Problem Analysis

Mathematical Concepts

Infinite Series
P-Series Test
Convergence and Divergence

Formulas

Sum of series: ∑ (n^p / n^q) = ∑ n^{p-q}
P-Series Test: ∑ 1/n^r, where r > 1 converges and r ≤ 1 diverges

Theorems

P-Series Test

Suitable Grade Level

University Level