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Use the test of your choice to determine whether the following series converge. $$\sum_{k=1}^{\infty} \frac{1}{\sqrt{k^{3}-k+1}}$$

Short Answer

Expert verified
Answer: The series converges.

Step by step solution

01

Identify the series to compare with

The given series is: $$\sum_{k=1}^{\infty} \frac{1}{\sqrt{k^{3}-k+1}}$$ To apply the Limit Comparison Test, we should find a known converging series to compare it with. A suitable candidate is: $$\sum_{k=1}^{\infty} \frac{1}{k^{\frac{3}{2}}}$$ This series converges because it is a p-series with p = 3/2 > 1.
02

Compute the limit for the Limit Comparison Test

To apply the Limit Comparison Test, we need to compute the limit of the ratio between the series terms: $$\lim_{k \to \infty} \frac{\frac{1}{\sqrt{k^{3}-k+1}}}{\frac{1}{k^{\frac{3}{2}}}}$$ Simplify the expression and calculate the limit: $$\lim_{k \to \infty} \frac{k^{\frac{3}{2}}}{\sqrt{k^{3}-k+1}}$$
03

Apply the Limit Comparison Test

Evaluate the limit by considering the asymptotic behavior of the terms. As k approaches infinity, the dominant term in the denominator is $$k^{3}$$ Thus, the limit will be: $$\lim_{k \to \infty} \frac{k^{\frac{3}{2}}}{\sqrt{k^{3}}}$$ Simplifying the expression: $$\lim_{k \to \infty} \frac{k^{\frac{3}{2}}}{k^{\frac{3}{2}}}$$ The limit evaluates to 1, which is a positive finite number.
04

Apply the conclusion of the Limit Comparison Test

Since the limit from Step 3 is a positive finite number and the comparison series $$\sum_{k=1}^{\infty} \frac{1}{k^{\frac{3}{2}}}$$ is known to converge, by the Limit Comparison Test, the given series: $$\sum_{k=1}^{\infty} \frac{1}{\sqrt{k^{3}-k+1}}$$ also converges.

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Key Concepts

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

Convergence of Series
Understanding the convergence of series is fundamental in the study of infinite series. Simply put, if the sum of an infinite series approaches a specific value as the number of terms increase, we say the series converges. To ascertain convergence, we have various tests, one of which is the Limit Comparison Test. This test is particularly beneficial when dealing with a complex series whose convergence isn't immediately apparent.

The Limit Comparison Test involves comparing the series in question to a simpler 'comparison series' that we already understand well. If the ratio of the nth terms of the two series approaches a positive, finite limit as n goes to infinity, and the comparison series converges, then the original series converges as well.
P-Series
A p-series is an infinite series of the form \[\sum_{k=1}^{\rm{\infty}} \frac{1}{k^p}\], where p is a constant. The convergence of a p-series is determined by the value of p. If p greater than 1, the series converges; if p is less than or equal to 1, the series diverges. This behavior is due to the integral test, another useful method for testing convergence, which shows us that the integral of 1/x^p converges only when p > 1.

When we encounter a series that is not immediately recognizable as a p-series, we might compare it to a p-series to use the properties of the p-series to determine convergence of the original series.
Infinite Series
An infinite series is a sum of an infinite number of terms. They can be daunting, because unlike finite sums, we cannot simply 'add up' all the terms. Instead, we look for patterns and use tests to determine if adding infinitely many terms will 'settle down' to a finite value. The series given in the exercise, \[\sum_{k=1}^{\rm{\infty}} \frac{1}{\sqrt{k^3-k+1}}\], is an example of such a series where direct calculation of the sum isn't feasible. Instead, we use tests like the Limit Comparison Test to determine the behavior of such infinite sums.
Asymptotic Behavior
The term 'asymptotic behavior' refers to the behavior of a function as the variable goes to infinity. In terms of series, we often look at how the nth term behaves as n becomes very large to understand the properties of the entire series. In the context of the Limit Comparison Test, we look at the leading term because it dominates the behavior of the function for large values of n. In the exercise, the \(k^3\) term in the denominator is the dominant term. When comparing the terms of two series as n approaches infinity, we often focus on these dominant, or 'asymptotic', terms to simplify our comparison and reach a conclusion about convergence.

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Most popular questions from this chapter

A heifer weighing 200 lb today gains 5 lb per day with a food cost of \(45 \mathrm{c} /\) day. The price for heifers is \(65 \mathrm{q} / \mathrm{lb}\) today but is falling \(1 \% /\) day. a. Let \(h_{n}\) be the profit in selling the heifer on the \(n\) th day, where \(h_{0}=(200 \mathrm{lb}) \cdot(\$ 0.65 / \mathrm{lb})=\$ 130 .\) Write out the first 10 terms of the sequence \(\left\\{h_{n}\right\\}\). b. How many days after today should the heifer be sold to maximize the profit?

Use the ideas of Exercise 88 to evaluate the following infinite products. $$\text { a. } \prod_{k=0}^{\infty} e^{1 / 2^{k}}=e \cdot e^{1 / 2} \cdot e^{1 / 4} \cdot e^{1 / 8} \dots$$ $$\text { b. } \prod_{k=2}^{\infty}\left(1-\frac{1}{k}\right)=\frac{1}{2} \cdot \frac{2}{3} \cdot \frac{3}{4} \cdot \frac{4}{5} \cdots$$

Use Theorem 8.6 to find the limit of the following sequences or state that they diverge. $$\left\\{\frac{3^{n}}{n !}\right\\}$$

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 \(c_{0}=100\)

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 \(\left\\{S_{n}\right\\}\) $$h_{0}=20, r=0.75$$

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