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Converge, and which diverge? Give reasons for your answers. (When you check an answer, remember that there may be more than one way to determine the series' convergence or divergence.) $$\sum_{n=1}^{\infty}\left(1+\frac{1}{n}\right)^{n}$$

Short Answer

Expert verified
The series diverges because the terms approach \( e \) as \( n \to \infty \).

Step by step solution

01

Identify the Series

We are given the infinite series \( \sum_{n=1}^{\infty} \left(1 + \frac{1}{n}\right)^n \). Our goal is to determine if this series converges or diverges.
02

Apply the Limit Comparison Test

The terms of the series given are \( a_n = \left(1 + \frac{1}{n}\right)^n \). As \( n \to \infty \), by the definition of \( e \), \( \left(1 + \frac{1}{n}\right)^n \) approximates \( e \), which is a constant greater than 1. Therefore, \( a_n \to e \). Since the limit is a positive constant, not zero, the series diverges by the term test. The divergent behavior of \( a_n \) suggests that the series diverges.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Limit Comparison Test
The Limit Comparison Test is a valuable tool when analyzing the convergence or divergence of an infinite series. Essentially, this test helps us to compare a series we are interested in (\( \sum a_n \)) with a known benchmark series (\( \sum b_n \)). The idea is to evaluate the behavior of the terms by looking at the limit\[ L = \lim_{{n \to \infty}} \frac{a_n}{b_n} \]where \( a_n \) and \( b_n \) are terms from the two series being compared. If this limit \( L \) is a finite positive number, both series will typically either converge or diverge together. In our specific exercise, the terms given were compared to the constant 1 instead. Since \( a_n \) tends to a constant \( e \), and not zero, it directly indicates divergence by a related result: the Term Test. The strength of the Limit Comparison Test lies in its ability to reduce a complex unknown series into a simpler form which can be more easily evaluated by comparison to a known standard.
Divergence
Divergence in the context of an infinite series means that the sum of the series does not settle to a finite number as you include more and more terms. More simply put, no matter how far you extend the sum of the series—by adding more terms— it doesn't approach a particular value. In our example, the series \( \sum_{n=1}^{\infty} \left(1 + \frac{1}{n}\right)^n \) generates terms that approach a constant \( e \). Since this limit isn’t zero, divergent nature is established.A crucial aspect of series analysis is determining divergence to prevent assuming a finite sum where there isn’t one. This exercise perfectly illustrates divergence using the Term Test, emphasizing why even a firm understanding of limits is essential for assessing series.
Term Test
The Term Test is a fundamental tool for checking the divergence of a series. According to the test, if the limit of the sequence of terms \( a_n \) of a series does not equal zero:\[ \lim_{{n \to \infty}} a_n eq 0 \]then the series \( \sum a_n \) diverges.In the problem at hand, \( a_n = \left(1 + \frac{1}{n}\right)^n \) converges to the constant \( e \), which is not zero. Hence, the series fails the Term Test for convergence, confirming its divergence.The power of the Term Test lies in its straightforward nature. When the terms of a series don't vanish to zero, they ultimately contribute enough to keep a finite sum elusive. It provides an immediate check before diving into more detailed analysis with other tests.

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