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Determine whether the following series converge. $$\sum_{k=0}^{\infty} \frac{(-1)^{k}}{k^{2}+10}$$

Short Answer

Expert verified
Question: Determine if the following series converges or diverges: $$\sum_{k=0}^{\infty} \frac{(-1)^{k}}{k^2 + 10}$$ Answer: Converges.

Step by step solution

01

Write the general term of the series

The general term of the series is given by: $$a_k = \frac{(-1)^k}{k^2 + 10}$$
02

Show that the absolute values of the terms are non-increasing

First, we'll look at the function \(f(k) = \frac{1}{k^2+10}\), which represents the absolute value of the term \(a_k\). We want to show that \(f(k+1) \leq f(k)\) for all \(k\). Now, let's find the first derivative of \(f(k)\): $$f'(k) = -\frac{2k}{(k^2+10)^2}$$ Since \(k^2+10>0\) and \((k^2+10)^2>0\) for all \(k\), we can see that \(f'(k) \leq 0\) for all \(k\). Hence, \(f(k)\) is non-increasing. This implies that the absolute values of the terms are non-increasing: $$|a_{k+1}| \leq |a_k|$$
03

Show that the limit of the absolute value of the terms approaches zero

Now, let's find the limit of the absolute value of \(a_k\) as \(k\) goes to infinity: $$\lim_{k \to \infty} |a_k| = \lim_{k \to \infty} \frac{1}{k^2+10}$$ As \(k\) goes to infinity, \(k^2+10\) also goes to infinity. Thus: $$\lim_{k \to \infty} \frac{1}{k^2+10} = 0$$
04

Conclude using the Alternating Series Test

Since both conditions of the Alternating Series Test are satisfied – the absolute values of the terms are non-increasing and the limit of the absolute value of the terms approaches zero as \(k\) goes to infinity – we can conclude that the given series converges: $$\sum_{k=0}^{\infty} \frac{(-1)^{k}}{k^{2}+10}$$ converges.

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