Chapter 9: Problem 41
Using the Root Test In Exercises \(39-52,\) use the Root Test to determine the convergence or divergence of the series. $$\sum_{n=1}^{\infty}\left(\frac{3 n+2}{n+3}\right)^{n}$$
Short Answer
Expert verified
The series \(\sum_{n=1}^{\infty}\left(\frac{3n+2}{n+3}\right)^{n}\) diverges.
Step by step solution
01
Understanding the Root Test
The Root Test is a method used to test for the convergence/divergence of an infinite series. According to the Root Test, if we have \(\lim_{n \to \infty} \sqrt[n]{|a_n|} = L\), then the series \(\sum_{n}a_n\) will converge if \(L<1\), diverge if \(L>1\) and be inconclusive if \(L=1\)
02
Apply the Root Test
Let's apply the Root Test to the given series. We need to calculate the limit \(\lim_{n \to \infty} \sqrt[n]{\left|\frac{3n+2}{n+3}\right|^{n}}\). This simplifies to \(\lim_{n \to \infty} \frac{3n+2}{n+3}\).
03
Calculate the Limit
To find the limit \(\lim_{n \to \infty} \frac{3n+2}{n+3}\), we can divide the numerator and the denominator by n, the highest power in the denominator, to get \(\lim_{n \to \infty} \frac{3 + \frac{2}{n}}{1 + \frac{3}{n}}\). As \(n\) approaches infinity, \(\frac{2}{n}\) and \(\frac{3}{n}\) approach 0, so the limit is \(L = \frac{3 + 0}{1 + 0} = 3\).
04
Determine Convergence/Divergence
Since the limit \(L = 3\) is greater than 1, by the Root Test, the series \(\sum_{n=1}^{\infty}\left(\frac{3n+2}{n+3}\right)^{n}\) diverges.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Convergence
The concept of convergence in mathematics, particularly with series, describes a situation where the sum of infinite terms approaches a definite value as more terms are added. When dealing with infinite series, checking for convergence is crucial.
- A series is said to converge if the sum of its terms moves towards a specific, finite number.
- Common tests for checking convergence include the Root Test, Ratio Test, and Integral Test.
- Convergence is essential because it indicates whether the series accumulates to a meaningful result or not. If it converges, it means you can find a finite sum.
Divergence
Divergence is the opposite of convergence. In the realm of infinite series, this term is used when the sums of the series do not settle towards a fixed, finite number as more terms are added. Instead, they continue to grow without bound or oscillate without settling.
- A diverging series will not settle on a finite sum, rendering it useless for calculations intending to achieve a stable value.
- The Root Test, among others, is a tool to identify divergence by checking the limit of the sequence’s terms.
- If the limit result during the Root Test is greater than one, as in the case of our example, the series is said to diverge.
Infinite Series
An infinite series is a sum of infinitely many terms, expressed as \(\sum_{n=1}^{fty} a_n\). In the world of mathematics, such series often model real-world phenomena and complex mathematical processes.
- Infinite series can be daunting but are incredibly useful in representing complex ideas concisely and computationally.
- Understanding whether an infinite series converges or diverges is key to determining its usefulness in calculations and predictions.
- Typical evaluations involve determining the characteristic behavior of the series terms as they extend to infinity.
Limit Calculation
Calculating limits is a fundamental process in mathematics, particularly when dealing with series and sequences. It helps determine the behavior of terms as they approach infinity.
- Limits help identify the eventual behavior of a function or series, providing essential information for making conclusions about convergence or divergence.
- In the Root Test example, we calculated the limit to be 3 by simplifying the expression \(\lim_{n \to \infty} \frac{3n+2}{n+3}\) by factoring and canceling relevant terms.
- This calculation showed how the series behaves as we reach larger values of \(n\), determining the final decision regarding divergence.