Determine convergence for a series

In summary, the conversation discusses finding the convergence or divergence of the series sum ln n/(ln(ln n)) from n=3 to infinity. The person believes it diverges and plans to use the limit test, but is unsure what to compare it to. Using 1/n in the limit comparison test is suggested, as well as noticing that log(n) is larger than log(log(n)) for most values of n. It is also noted that the tail of the series does not approach 0 and the nth term test for divergence may be applicable.
  • #1
MozAngeles
101
0

Homework Statement


Sum ln n/(ln(ln n)) n=3..infinity?
Im pretty sure it diverges and I am pretty sure to use the limit test but i just don't know what to compare this sum to. Would 1/n be ok. Do i have to justify why they are similar?

ANy help would be nice thanks.


Homework Equations





The Attempt at a Solution

 
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  • #2
MozAngeles said:

Homework Statement


Sum ln n/(ln(ln n)) n=3..infinity?
Im pretty sure it diverges and I am pretty sure to use the limit test but i just don't know what to compare this sum to. Would 1/n be ok. Do i have to justify why they are similar?

ANy help would be nice thanks.
Sure, you can use 1/n in the limit comparison test.

If this limit is positive, then your series diverges.
[tex]\lim_{n \to \infty}\frac{\frac{ln(n)}{ln(ln(n))}}{1/n}[/tex]
 
  • #3
You could also just see that log(n) is larger than log(log(n)) for basically every n you're using, and so you're summing a sequence of numbers that all are greater than 1. So realistically, you could use a limit comparison with 1.
 
  • #4
even worse, the tail of this series doesn't seem to go to 0, log(x) will grow faster than log(log(x))
 
  • #5
Char. Limit said:
You could also just see that log(n) is larger than log(log(n)) for basically every n you're using, and so you're summing a sequence of numbers that all are greater than 1. So realistically, you could use a limit comparison with 1.

wisvuze said:
even worse, the tail of this series doesn't seem to go to 0, log(x) will grow faster than log(log(x))

These observations suggest that the nth term test for divergence might be appropriate here.
 
  • #6
thanks i figured it out like two seconds after i posted. haha
 

Related to Determine convergence for a series

What is a series and how is it related to convergence?

A series is a mathematical expression that consists of a sequence of terms added together. Convergence refers to the behavior of a series and whether the sum of its terms approaches a finite value or not.

What does it mean for a series to converge?

A series is said to converge if the sum of its terms approaches a finite value as the number of terms increases. In other words, the series has a well-defined finite limit.

How can I determine if a series converges or not?

There are several tests that can be used to determine the convergence of a series, such as the ratio test, the comparison test, and the integral test. These tests involve analyzing the behavior of the terms in the series and can help determine if the series converges or diverges.

What is the difference between absolute and conditional convergence?

Absolute convergence occurs when the series converges regardless of the order in which its terms are added. On the other hand, conditional convergence occurs when the series only converges if its terms are added in a specific order.

What happens if a series does not converge?

If a series does not converge, it is said to diverge. This means that the sum of its terms does not approach a finite value and the behavior of the series is unpredictable. Divergent series can still have useful properties and applications, but they do not have a well-defined finite limit.

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