Proving a limit theorem of a sequence (square root)

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Homework Help Overview

The discussion revolves around proving that if a sequence {a_n} converges to a non-zero limit A, then the limit of the square root of the sequence, sqrt(a_n), converges to sqrt(A). Participants are exploring the properties of limits and the behavior of sequences under square root transformations.

Discussion Character

  • Exploratory, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss the application of the epsilon-delta definition of limits, with attempts to manipulate inequalities involving square roots. There are questions about bounding expressions and ensuring the conditions for applying limit theorems are met.

Discussion Status

The conversation includes various attempts to clarify the proof structure and the necessary conditions for convergence. Some participants suggest specific approaches to handle the inequalities, while others express uncertainty about their reasoning or the arrangement of their arguments. There is ongoing exploration of the implications of assuming A > 0 and how to handle cases where A = 0.

Contextual Notes

Participants note the importance of ensuring that the terms involved in the limits are non-negative, as the square root function is only defined for non-negative numbers in the context of real sequences. There is also a mention of needing to specify the relationship between different epsilon values and their corresponding N values in the proof.

  • #31
aatzn said:
Anyway 1 is not the limit of your sequence, there is no limit for your example.

You do not know that your sequence \sqrt{a_n} has a limit, either. That is what you are trying to prove! Please state precisely what your theorem says.
 
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  • #32
The theorem says that the limit of a sequence product of two other sequences
(with finite limits!) is the product of their limits.
So, in our case ( \lim a_n = A ), if
\lim \sqrt{a_n}
exists finite, than it is
\sqrt{A}
 
  • #33
aatzn said:
So, in our case ( \lim a_n = A ), if
\lim \sqrt{a_n}
exists finite, than it is
\sqrt{A}

But you didn't prove that \lim \sqrt{a_n} exists.
 
  • #34
You are right.
My weaker demonstration shows how that limit should be, if it exists.
On the other hand, with the previous demonstration not only we know the form of the hypothetical limit, but we are sure that it always exists.
But your sample? what did you mean with post n. #30?
Anyway don’t you think my simple method could be a useful aid for the study of more complicate sequences with nth roots?
 
Last edited:

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