Finding Partial Limits of a Sequence: A Homework Challenge

In summary, the problem is to find all the partial limits of a sequence where a1 = 0, a2n = an/3, and a2n+1 = 1/3 + an. Both subsequences of odd and even terms are monotonic and have suprimums, but the approach to proving this was initially incorrect. The correct calculation of the first few terms showed that both subsequences are monotonic, leading to the solution.
  • #1
estro
241
0

Homework Statement


I have to find all the partial limits {I hope this is how this term named in English} of a sequences

Homework Equations


[tex]a_1=0[/tex]

[tex]a_{2n}=\frac {a_{2n-1}} {3}[/tex]

[tex] a_{2n+1} = 1/3 + a_{2n}[/tex]

The Attempt at a Solution


I have tried to prove first that sequences of all the even terms converges due to fact that sequence is monotonic and have a suprimum, but have failed to prove it.
Another problem is that subsequences of odd term is non monotonic, but I also can't use the Cantor's Lemma.

Could you please suggest how to approach this problem?
Thanks.
 
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  • #2
estro said:

Homework Statement


I have to find all the partial limits {I hope this is how this term named in English} of a sequences


Homework Equations


[tex]a_1=0[/tex]

[tex]a_{2n}=\frac {a_{2n-1}} {3}[/tex]

[tex] a_{2n+1} = 1/3 + 2_{2n}[/tex]
In the equation above do you mean a2n+1 = 1/3 + 22n?
estro said:

The Attempt at a Solution


I have tried to prove first that sequences of all the even terms converges due to fact that sequence is monotonic and have a suprimum, but have failed to prove it.
Another problem is that subsequences of odd term is non monotonic, but I also can't use the Cantor's Lemma.

Could you please suggest how to approach this problem?
Thanks.
 
  • #3
Sorry, have fixed it in my first post.
 
  • #4
You're looking at the two subsequences: one with the odd-index terms and the other with the even-index terms. Have you calculated the first dozen or so terms of your sequence?
 
  • #5
I've calculated again some terms of the sequence and found out that I did a mistake in my previous calculation as both subsequences seem to be monotonic, but I can't find a way to prove that the sequences have suprimums.

0, 0, 81/243, 27/243, 108/243, 36/243, 36/243, 117/243, 39/243, 120/243, 40/243, 121/243
 
  • #6
I have figured it out, thanks.
 

Related to Finding Partial Limits of a Sequence: A Homework Challenge

1. What is a partial limit of a sequence?

A partial limit of a sequence is a value that the terms of a sequence approach as the number of terms increases towards infinity. It is not necessarily the actual limit of the sequence, but it is a value that the terms of the sequence get closer to as the sequence progresses.

2. How do you find the partial limit of a sequence?

To find the partial limit of a sequence, you can either use a formula or a graphing calculator. The formula involves taking the limit as n approaches infinity of the nth term of the sequence. The graphing calculator can also be used to plot the terms of the sequence and visually determine the partial limit.

3. Why is it important to find the partial limit of a sequence?

Finding the partial limit of a sequence can help us understand the behavior of the sequence as the number of terms increases. It can also help us determine the actual limit of the sequence, which is important in many mathematical and scientific applications.

4. Can a sequence have more than one partial limit?

Yes, a sequence can have more than one partial limit. This occurs when the terms of the sequence fluctuate between two or more values as the number of terms increases towards infinity. In this case, the sequence does not have a single limit, but it has multiple partial limits.

5. Are there any shortcuts or tricks for finding the partial limit of a sequence?

There are some strategies that can make finding the partial limit of a sequence easier, such as noticing patterns in the terms of the sequence or using known limits of basic sequences. However, there is no universal shortcut or trick that can be applied to all sequences, so it is important to understand the concept and use appropriate methods for each individual sequence.

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