Convergence Proof: Showing (\sqrt{x_{n}})\rightarrow0

In summary: It is a slightly more complicated theorem but it is still a limit theorem. The proof is a little more involved and I'm not sure if the OP would be able to do it.
  • #1
kathrynag
598
0

Homework Statement


Let [tex]x_{n\geq}[/tex]0 for all n in the natural numbers.
If ([tex]x_{n}[/tex])[tex]\rightarrow[/tex]0, show that ([tex]\sqrt{x_{n}}[/tex])[tex]\rightarrow[/tex]0.



Homework Equations





The Attempt at a Solution


So far, I have started with [tex]\left|\sqrt{x_{n}}-0\right|[/tex]. Not sure if that's the right way to start.
 
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  • #2
You should probably start with the definition of convergence
 
  • #3
A sequence converges to a real number a if for every positive [tex]\epsilon[/tex], there exists an N element of the natural numbers such that whenever n[tex]\geq[/tex]N, it follows that [tex]\left|a_{n}-a\right|[/tex]<[tex]\epsilon[/tex].
 
  • #4
[tex] a^{2} \leq b^{2}[/tex] iff [tex] a \leq b[/tex]

[tex] a,b \geq 0[/tex]

Can you use this ?
 
  • #5
Then the sequence is less than 0 and thus converges to 0
 
  • #6
How did you arrive at such a conclusion? Btw what you said not correct.

How is the sequence less than zero ? In your definition [tex] x_{n} \geq 0[/tex].
 
  • #7
so the sequence is greater than 0 because x is greater than 0.
 
  • #8
All I wanted you to do wanted you to do was take the square root of both sides of the inequality...
[tex] x_{n} < \epsilon [/tex].
 
  • #9
If g(x) --> A when x --> a then p(g(x)) --> p(A) when x --> a.
 
  • #10
Hmm... what if p was the square root function and A was negative. ?
 
  • #11
Well A needs to be in the domain of p for it to make sense. Guess I should have written that..
 
  • #12
It's fine. Btw this theorem is not one of the 4 limit theorems given in most analysis books so I doubt the OP can use it. OP would need to prove it to use it.
 
  • #13
We had 5 limit theorems when I did analysis in first year at uni. The proof is like 3 lines and not harder than the rest so I think it is strange it isn't standard at other places
 
  • #14
I think you are referring to limits of functions not limit theorems. The limit theorems are for sequences and they are later generalized to functions.
I am taking analysis right now and the thoerem you mentioned is in the limit of functions section
 

1. What is convergence proof?

Convergence proof is a mathematical technique used to show that a sequence of numbers or functions approaches a specific value or limit. It is used to prove the convergence of a series or the convergence of a sequence to a limit.

2. What does it mean for a sequence to converge?

When a sequence converges, it means that as the number of terms in the sequence increases, the terms get closer and closer to a specific value or limit. In other words, the sequence approaches a specific value as the number of terms increases.

3. How is convergence proof used in mathematics?

Convergence proof is used in various areas of mathematics, such as analysis, calculus, and number theory. It is an essential tool for proving the convergence of series and sequences, which are fundamental concepts in these fields of mathematics.

4. What is the purpose of showing (\sqrt{x_{n}})\rightarrow0 in convergence proof?

The purpose of showing (\sqrt{x_{n}})\rightarrow0 is to prove that the sequence of numbers represented by \sqrt{x_{n}} approaches 0 as the number of terms increases. This is an important result in many mathematical applications, and it is often used as a building block for more complex convergence proofs.

5. What are the key steps in a convergence proof for showing (\sqrt{x_{n}})\rightarrow0?

The key steps in a convergence proof for showing (\sqrt{x_{n}})\rightarrow0 typically include defining the sequence, identifying a suitable limit, and then using mathematical techniques such as the squeeze theorem, the ratio test, or the comparison test to show that the sequence approaches the desired limit. The specific steps may vary depending on the specific sequence and the chosen method of proof.

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