Math Problem Statement

Determine the convergence or divergence of the series \( \sum_{k=1}^\infty \frac{2\sqrt{k}}{4k - 3} \) using the comparison test.

Solution

The image contains a problem about determining the convergence or divergence of a series using the comparison test. Let me analyze it step by step and summarize the reasoning behind convergence or divergence.Here’s a breakdown of the given problem and solution:

1. Series Under Analysis

The given series is: k=12k4k3.\sum_{k=1}^\infty \frac{2\sqrt{k}}{4k - 3}.

2. Terms of the Series and Downward Comparison

Using the inequality 4k3<4k4k - 3 < 4k, we estimate: 2k4k3>2k4k.\frac{2\sqrt{k}}{4k - 3} > \frac{2\sqrt{k}}{4k}. Simplifying the right-hand side: 2k4k=12kk=12k1/2.\frac{2\sqrt{k}}{4k} = \frac{1}{2} \cdot \frac{\sqrt{k}}{k} = \frac{1}{2k^{1/2}}. This means the terms are bounded below by a series proportional to 1k1/2\frac{1}{k^{1/2}}, which is a divergent pp-series (p=1/2<1p = 1/2 < 1).

3. Upward Comparison

Using 4k3>3k4k - 3 > 3k, we estimate: 2k4k3<2k3k.\frac{2\sqrt{k}}{4k - 3} < \frac{2\sqrt{k}}{3k}. Simplifying: 2k3k=231k1/2.\frac{2\sqrt{k}}{3k} = \frac{2}{3} \cdot \frac{1}{k^{1/2}}. This bounds the terms above by another divergent pp-series 1k1/2\frac{1}{k^{1/2}}.

4. Comparison Test

To apply the comparison test, compare with the series: k=11k1/2.\sum_{k=1}^\infty \frac{1}{k^{1/2}}. Since both the lower and upper bounds are divergent pp-series, the original series also diverges by the comparison test.

5. Claim and Conclusion

The series k=12k4k3\sum_{k=1}^\infty \frac{2\sqrt{k}}{4k - 3} diverges.

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Math Problem Analysis

Mathematical Concepts

Series
Convergence and Divergence
Comparison Test
Inequalities

Formulas

Comparison test for series
Bound estimations: \( \frac{2\sqrt{k}}{4k - 3} > \frac{1}{2k^{1/2}} \) and \( \frac{2\sqrt{k}}{4k - 3} < \frac{2}{3k^{1/2}} \)

Theorems

Comparison Test for Series

Suitable Grade Level

Undergraduate Mathematics