Determine whether series is convergent or divergent

In summary, the conversation discusses whether the series \sum^{\infty}_{n=1} \frac{1}{\sqrt{n+1}+\sqrt{n}} converges. One approach suggested is to rationalize the denominators, but it is pointed out that this assumption may not be valid. Another approach is to compare the series with a known divergent p-series.
  • #1
Nan1teZ
11
0

Homework Statement



Determine whether or not the series [tex]\sum^{\infty}_{n=1} \frac{1}{\sqrt{n+1}+\sqrt{n}}[/tex] converges.

The Attempt at a Solution



Assuming this diverges, I rationalize it to get get [tex]\sum^{\infty}_{n=1} \sqrt{n+1} - \sqrt{n}[/tex]. How would I proceed further?

Is this even the right approach?
 
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  • #2
Well, you can't just assume it diverges. I haven't studied series in quite a while. The rationalizing of the denominators seems like a promising approach, but someone else will have to comment on that.

I think the following is a valid method. Let f(n) be the expression we are summing. As n-> +inf f(n) -> 1/(2sqrt(n)). But the infinite series with 1/sqrt(n) is a p-series and I think it's divergent.
 
  • #3
snipez90 is right. Don't 'rationalize' it. Just compare it with a divergent p-series.
 

1. What is the difference between a convergent and a divergent series?

A convergent series is one that has a finite limit or sum, while a divergent series is one that does not have a finite limit or sum. In simpler terms, a convergent series "converges" or approaches a specific value, while a divergent series does not.

2. How do you determine if a series is convergent or divergent?

There are several methods for determining the convergence or divergence of a series, including the comparison test, ratio test, and integral test. These tests involve evaluating the behavior of the terms in the series and comparing them to known convergent or divergent series.

3. What is the role of the limit in determining the convergence or divergence of a series?

The limit plays a crucial role in determining the convergence or divergence of a series. If the limit of the series approaches a specific finite value, then the series is convergent. However, if the limit does not exist or approaches infinity, then the series is divergent.

4. Can a series be both convergent and divergent?

No, a series cannot be both convergent and divergent. A series can only have one of these two characteristics. However, there are cases where a series may appear to be convergent or divergent, but upon further investigation, it is found to be neither.

5. Are there any real-world applications for determining the convergence or divergence of a series?

Yes, there are several real-world applications for determining the convergence or divergence of a series. For example, in finance, analyzing the convergence or divergence of a series can help determine the profitability of an investment. In physics, it can help determine the behavior of a system over time. In engineering, it can help determine the stability or instability of a system.

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