Does the series converge or diverge?

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Homework Help Overview

The discussion revolves around determining the convergence or divergence of the series \(\sum_{n=1}^{\infty} \frac{1}{n+\sqrt{n}}\). Participants are exploring various convergence tests in the context of series analysis.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • The original poster expresses frustration with the root and ratio tests, mentioning attempts to compare the series with larger and smaller series. Some participants suggest the integral test and provide a comparison to \(2n\). Others question the application of the integral test and the implications of the comparison to the divergent harmonic series \(1/2n\).

Discussion Status

Participants are actively engaging with different tests and comparisons. There is a mix of confusion and clarification regarding the integral test and the comparison test, with some expressing satisfaction with the conclusions drawn about divergence, while others seek further understanding of the reasoning behind the comparisons.

Contextual Notes

There is an ongoing discussion about the validity of the comparisons made and the assumptions underlying the tests being applied. The original poster's struggle with the tests indicates a need for deeper exploration of the convergence criteria.

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Homework Statement



Determine whether the series [tex]\sum_{n=1}^{\infty} \frac{1}{n+\sqrt{n}}[/tex]
converges or diverges.

Homework Equations





The Attempt at a Solution



This is driving me nuts. I get nowhere with the root test or the ratio test. I can think of some larger series that diverge (no good) and some smaller series that converge (also no good). What test would you recommend?
 
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The integral test.

n+√n < n+n = 2n

[tex]\frac{1}{n + \sqrt{n}} > \frac{1}{2n}[/tex]
 
I'm confused. Doesn't the integral test have us say that if [tex]\int_{1}^{\infty}{\frac{1}{n+\sqrt{n}} dn}[/tex] diverges, then our series diverges?

Where do you get the 2n from using the integral test?

Also, the relation [tex]n + \sqrt{n} \leq n+n[\tex] definitely holds, but isn't the series of 1/2n from n=1 to infinity a divergent harmonic series?[/tex]
 
Ah, well, I suppose in either case, it's a divergent series. This makes me very happy. Thanks.
 
I should have said the the comparison test with the integral test . Sorry about any confusion.

1/2n diverges, and since it is greater than 1/(n+√n), the latter also diverges.
 

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