Chapter 9: Problem 13
Determine convergence or divergence for each of the series. Indicate the test you use. $$ \sum_{n=1}^{\infty} \frac{n+3}{n^{2} \sqrt{n}} $$
Short Answer
Expert verified
The series converges by the p-series test.
Step by step solution
01
Simplify the Series Terms
Consider the series \( \sum_{n=1}^{\infty} \frac{n+3}{n^{2} \sqrt{n}} \). First, simplify the terms: \( \frac{n+3}{n^{2} \sqrt{n}} = \frac{n}{n^{2} \sqrt{n}} + \frac{3}{n^{2} \sqrt{n}} \). This simplifies to \( \frac{1}{n^{3/2}} + \frac{3}{n^{5/2}} \).
02
Compare with a Known Series
Decompose the simplified terms into two separate series: \( \sum \frac{1}{n^{3/2}} \) and \( \sum \frac{3}{n^{5/2}} \). Recognize these as p-series, where \( p = 3/2 \) and \( p = 5/2 \), respectively.
03
Determine Convergence of the Series
For a p-series \( \sum \frac{1}{n^p} \), the series converges if \( p > 1 \). Here, both \( \frac{1}{n^{3/2}} \) and \( \frac{3}{n^{5/2}} \) have \( p > 1 \). Therefore, both series converge.
04
Conclusion of the Series' Convergence
Since both the series \( \sum \frac{1}{n^{3/2}} \) and \( \sum \frac{3}{n^{5/2}} \) converge, their sum, \( \sum \left( \frac{1}{n^{3/2}} + \frac{3}{n^{5/2}} \right) \), also converges.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
p-series test
The p-series test is a well-known method used to determine the convergence or divergence of a series. A p-series takes the form of \( \sum \frac{1}{n^p} \). Here, \( p \) is a positive constant that plays a crucial role in assessing whether the series converges or diverges.
For convergence of a p-series, the value of \( p \) must be greater than 1. If \( p > 1 \), the series converges. If \( p \leq 1 \), the series diverges.
For convergence of a p-series, the value of \( p \) must be greater than 1. If \( p > 1 \), the series converges. If \( p \leq 1 \), the series diverges.
- Example: \( \sum \frac{1}{n^2} \) converges because \( p = 2 \), which is greater than 1.
- In contrast, \( \sum \frac{1}{n} \) diverges as \( p = 1 \), which does not satisfy the convergence condition.
mathematical series
A mathematical series is simply the sum of the terms of a sequence. In more formal terms, it is written as \( \sum_{n=1}^{\infty} a_n \), where \( a_n \) represents the individual terms of the sequence.
Series come in many forms, such as geometric series, harmonic series, or the ones discussed here: p-series. The calculation of their convergence or divergence is a fundamental part of calculus.
Elements of understanding series include:
Series come in many forms, such as geometric series, harmonic series, or the ones discussed here: p-series. The calculation of their convergence or divergence is a fundamental part of calculus.
Elements of understanding series include:
- Recognition of the type of series, whether it's geometric, harmonic, etc.
- Application of appropriate tests like p-series test, ratio test, or comparison test among others.
- Interpretation of series behavior as \( n \) approaches infinity, which directly affects convergence.
infinite series convergence
Infinite series convergence refers to whether the sum of an infinite series approaches a finite number as more terms are added. It's a vital concept in understanding the behavior of series in calculus.
To determine infinite series convergence, mathematicians employ various techniques:
To determine infinite series convergence, mathematicians employ various techniques:
- Comparison tests: Compare series terms with another series whose convergence is known.
- Ratio and root tests: Gauge how terms behave as \( n \) becomes very large, focusing on the idea of a limit.
- Integral test: Use integration to test the convergence by approximating the series as a function.
- P-Series test: Specifically applicable when series take the shape of a p-series.