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Use the Root Test to determine whether the following series converge. $$1+\left(\frac{1}{2}\right)^{2}+\left(\frac{1}{3}\right)^{3}+\left(\frac{1}{4}\right)^{4}+\dots$$

Short Answer

Expert verified
Answer: The Root Test is inconclusive in this case, as the limit L = 1. We cannot determine if the series converges or not using this test.

Step by step solution

01

Identify the general term of the series

Observe the given series: $$1+\left(\frac{1}{2}\right)^{2}+\left(\frac{1}{3}\right)^{3}+\left(\frac{1}{4}\right)^{4}+\dots$$ The general term can be expressed as: $$a_{k}=\left(\frac{1}{k}\right)^{k}$$
02

Calculate the limit L

In order to use the Root Test, we need to calculate the limit: $$L = \lim_{k\rightarrow\infty}\sqrt[k]{|a_{k}|} = \lim_{k\rightarrow\infty}\sqrt[k]{\left(\frac{1}{k}\right)^{k}}$$
03

Simplify the limit expression

By calculating the limit: $$L = \lim_{k\rightarrow\infty} \frac{1}{\sqrt[k]{k}}$$
04

Evaluate the limit

To evaluate the limit, we can use the fact that as k approaches infinity, \(\sqrt[k]{k}\) approaches 1, so the limit becomes: $$L = \lim_{k\rightarrow\infty} \frac{1}{1} = 1$$
05

Apply the Root Test

Since the limit L = 1, the Root Test is inconclusive in this case. We cannot determine from this test whether the series converges or not. The student may need to try another test to determine the convergence or divergence of this series.

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Key Concepts

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

Understanding Series Convergence
Series convergence is about determining whether the sum of all terms in an infinite series will reach a particular value or continue to grow indefinitely. In simpler terms, when we say a series converges, it means that as we keep adding more terms, the sum stays around a certain number rather than going off to infinity.
The main idea is that for a series to be useful, we want it to settle to a specific value. If the series converges, it means that there exists a real number that the series approaches as the number of terms increases infinitely. If it doesn't, the series is said to diverge, which means the sum of its terms will keep increasing without bound.
When analyzing series, especially with tests like the Root Test, understanding whether a series is convergent or divergent is crucial in many fields such as calculus and mathematical analysis.
General Term of a Series Explained
The general term of a series is the formula that allows us to express any term based on its position in the sequence. For the series provided in the exercise:
  • 1
  • \(\left(\frac{1}{2}\right)^{2}\)
  • \(\left(\frac{1}{3}\right)^{3}\)
  • \(\left(\frac{1}{4}\right)^{4}\)
  • ... etc.
The general term can be written as \(a_{k} = \left(\frac{1}{k}\right)^{k}\). This term explains how each term in the sequence is generated based on its position (k) in the series.
To solve problems involving series, especially using tests for convergence, identifying this general term is often the first step in the analysis. The expression allows us to apply various tests, including the Root Test, to explore the behavior of the series as the sequence progresses.
The Process of Limit Evaluation
Limit evaluation is a fundamental concept used to determine the behavior of a function or sequence as it approaches a certain point. In the context of series and the Root Test, evaluating limits lets us examine how terms behave as the number of terms goes to infinity.
In the given exercise, the series uses the general term \(a_{k} = \left(\frac{1}{k}\right)^{k}\) and seeks to evaluate the limit: \[L = \lim_{k\rightarrow\infty}\sqrt[k]{|a_{k}|}\]
This translates to finding out how \(\sqrt[k]{\left(\frac{1}{k}\right)^{k}}\) behaves as k increases without bounds.
This process often involves simplifying expressions, applying limit laws, and sometimes employing other mathematical tools and principles to understand the trend the terms follow at the boundary of infinity.
What an Inconclusive Test Result Means
An inconclusive test result in series convergence indicates that the tool or test applied does not provide a definitive answer about whether the series converges or diverges. Using the Root Test in this example:\[L = \lim_{k\rightarrow\infty} \frac{1}{\sqrt[k]{k}} = 1\]
The test gives the result L = 1, which is one of the conditions where the Root Test does not conclusively tell us if a series converges or diverges.
This signifies that, while the Root Test is powerful for some series, it's not universal. When you receive an inconclusive result, like L = 1 in this case, you may need to use different convergence tests. Options such as the Ratio Test, Integral Test, or Comparison Test might offer the clarity needed to determine the series' behavior.
In practice, encountering an inconclusive result is a cue to explore other methods and deepen the understanding of the series in question.

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Most popular questions from this chapter

In the following exercises, two sequences are given, one of which initially has smaller values, but eventually "overtakes" the other sequence. Find the sequence with the larger growth rate and the value of \(n\) at which it overtakes the other sequence. $$a_{n}=\sqrt{n} \text { and } b_{n}=2 \ln n, n \geq 3$$

Consider the following situations that generate a sequence. a. Write out the first five terms of the sequence. b. Find an explicit formula for the terms of the sequence. c. Find a recurrence relation that generates the sequence. d. Using a calculator or a graphing utility, estimate the limit of the sequence or state that it does not exist. The Consumer Price Index (the CPI is a measure of the U.S. cost of living) is given a base value of 100 in the year \(1984 .\) Assume the CPI has increased by an average of \(3 \%\) per year since \(1984 .\) Let \(c_{n}\) be the CPI \(n\) years after \(1984,\) where \(c_{0}=100\)

Find the limit of the sequence $$\left\\{a_{n}\right\\}_{n=2}^{\infty}=\left\\{\left(1-\frac{1}{2}\right)\left(1-\frac{1}{3}\right) \cdots\left(1-\frac{1}{n}\right)\right\\}_{n=2}^{\infty}.$$

Marie takes out a \(\$ 20,000\) loan for a new car. The loan has an annual interest rate of \(6 \%\) or, equivalently, a monthly interest rate of \(0.5 \% .\) Each month, the bank adds interest to the loan balance (the interest is always \(0.5 \%\) of the current balance), and then Marie makes a \(\$ 200\) payment to reduce the loan balance. Let \(B_{n}\) be the loan balance immediately after the \(n\) th payment, where \(B_{0}=\$ 20,000\). a. Write the first five terms of the sequence \(\left\\{B_{n}\right\\}\). b. Find a recurrence relation that generates the sequence \(\left\\{B_{n}\right\\}\). c. Determine how many months are needed to reduce the loan balance to zero.

A ball is thrown upward to a height of \(h_{0}\) meters. After each bounce, the ball rebounds to a fraction r of its previous height. Let \(h_{n}\) be the height after the nth bounce and let \(S_{n}\) be the total distance the ball has traveled at the moment of the nth bounce. a. Find the first four terms of the sequence \(\left\\{S_{n}\right\\}\) b. Make a table of 20 terms of the sequence \(\left\\{S_{n}\right\\}\) and determine \(a\) plausible value for the limit of \(\left\\{S_{n}\right\\}\) $$h_{0}=20, r=0.5$$

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