42–76. Convergence or divergence Use a convergence test of your choice to determine whether the following series converge.
∑ (from k = 1 to ∞)k√k / k³

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First, rewrite the general term of the series to simplify it. The term is given as \(\frac{k \sqrt{k}}{k^3}\). Recall that \(\sqrt{k} = k^{1/2}\), so rewrite the term as \(\frac{k \cdot k^{1/2}}{k^3}\).

Combine the powers of \(k\) in the numerator: \(k \cdot k^{1/2} = k^{1 + 1/2} = k^{3/2}\). So the term becomes \(\frac{k^{3/2}}{k^3}\).

Simplify the fraction by subtracting exponents in the denominator from the numerator: \(k^{3/2 - 3} = k^{-3/2}\).

Now, the series can be written as \(\sum_{k=1}^\infty k^{-3/2}\). Recognize this as a p-series of the form \(\sum_{k=1}^\infty \frac{1}{k^p}\) where \(p = \frac{3}{2}\).

Apply the p-series convergence test: a p-series converges if and only if \(p > 1\). Since \(\frac{3}{2} > 1\), conclude that the series converges.

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Infinite Series and Convergence

An infinite series is the sum of infinitely many terms. Determining whether a series converges means checking if the sum approaches a finite limit as the number of terms grows indefinitely. Understanding convergence is essential to analyze the behavior of series like the one given.

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06:52

Convergence of an Infinite Series

Convergence Tests

Convergence tests are methods used to determine if an infinite series converges or diverges. Common tests include the Comparison Test, Ratio Test, Root Test, and p-Series Test. Choosing an appropriate test depends on the form of the series terms.

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Choosing a Convergence Test

Simplifying Series Terms

Before applying convergence tests, it is important to simplify the general term of the series. For example, rewriting k√k / k³ as k^(1 + 1/2) / k³ = k^(3/2) / k³ = k^(-3/2) helps identify the type of series and apply the correct convergence test.

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