Finding a limit of a sequence or proving it diverges

In summary, the conversation discusses finding the limit or proving the divergence of a sequence sin(1), cos(sin(1)), sin(cos(sin(1))) etc. Various equations and ideas are suggested, such as finding two subsequences with different limits or deducing equations for the limit value. Ultimately, it is concluded that the sequence must diverge since it must satisfy both sin(L)=L and cos(L)=L. The conversation ends with gratitude for the help provided.
  • #1
nikolafmf
114
0

Homework Statement



Given is a sequence: sin(1), cos(sin(1)), sin(cos(sin(1))) etc. Find the limit of the sequence or prove it diverges.

Homework Equations



?

The Attempt at a Solution



One way to prove a sequence diverges is to find two subsequences which converge to different limits, but I could not find such. I would be thankful for any idea :)
 
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  • #2
nikolafmf said:

Homework Statement



Given is a sequence: sin(1), cos(sin(1)), sin(cos(sin(1))) etc. Find the limit of the sequence or prove it diverges.


Homework Equations



?

The Attempt at a Solution



One way to prove a sequence diverges is to find two subsequences which converge to different limits, but I could not find such.


I would be thankful for any idea :)

If there is a limit L, then it must satisfy both sin(L)=L and cos(L)=L, mustn't it?
 
  • #3
Suppose it does converge to some value. What equations could you deduce regarding that value?
[Dick beat me to the Submit, and was a little more generous with the hint.]
 
  • #4
haruspex said:
Suppose it does converge to some value. What equations could you deduce regarding that value?
[Dick beat me to the Submit, and was a little more generous with the hint.]

Yeah, probably too generous in retrospect. I like yours better as a starter hint.
 
Last edited:
  • #5
Yes, it is true, it must satisfy both sin(L)=L and cos(L)=L, from which follows that the sequence diverges :)

Thank you very much to both for the help :)
 

FAQ: Finding a limit of a sequence or proving it diverges

What is a sequence?

A sequence is a list of numbers that follow a specific pattern or rule, usually denoted by the notation {an}, where n represents the position in the sequence and an represents the value at that position.

What does it mean for a sequence to converge or diverge?

A sequence converges if its terms approach a specific limit as n approaches infinity. This means that the values in the sequence get closer and closer to a single number as n gets larger. A sequence diverges if its terms do not approach a limit and instead continue to increase or decrease without bound.

How do you find the limit of a sequence?

To find the limit of a sequence, you can use the limit definition which states that a sequence converges to a limit L if for every positive number ε, there exists a natural number N such that for all n greater than N, the absolute value of the difference between the nth term and L is less than ε. You can also use various convergence tests, such as the Ratio Test or the Comparison Test, to determine the limit of a sequence.

What is the difference between proving a sequence converges and proving it diverges?

Proving a sequence converges requires showing that the terms of the sequence approach a specific limit as n approaches infinity. This can be done using the limit definition or convergence tests. On the other hand, proving a sequence diverges requires showing that the terms do not approach a limit and instead continue to increase or decrease without bound. This can be done by showing that the terms do not satisfy the conditions of convergence, such as the limit definition or convergence tests.

Why is it important to understand how to find the limit of a sequence or prove it diverges?

Understanding how to find the limit of a sequence or prove it diverges is important in many areas of mathematics, particularly in calculus and analysis. It allows us to determine the behavior of a sequence and make predictions about its values. This knowledge is also essential in solving real-world problems that involve sequences, as well as in understanding more complex mathematical concepts, such as series and continuity.

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