How can I use the given information to solve this problem?

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Homework Help Overview

The problem involves limits and continuity, specifically proving that if \( f(x) \geq 0 \) in a deleted neighborhood of \( c \) and \( \lim_{x \to a} f(x) = R \) with \( R > 0 \), then \( \lim_{x \to a} \sqrt{f(x)} = \sqrt{R} \). Participants are exploring the implications of these conditions and the mathematical reasoning required to establish the limit.

Discussion Character

  • Exploratory, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss the initial steps to manipulate the expression involving square roots and limits. There are attempts to apply limit definitions and explore the implications of the conditions given in the problem. Some participants express uncertainty about the correctness of their approaches and seek clarification on specific calculations.

Discussion Status

The discussion is ongoing, with participants providing insights and corrections to each other's reasoning. Some have offered guidance on how to approach the limit, while others are questioning the assumptions made regarding the limits and the conditions of the problem.

Contextual Notes

There is a noted confusion regarding the limits being taken, with one participant questioning whether the limit should be as \( x \to c \) instead of \( x \to a \). This indicates a potential misunderstanding of the problem setup that is being explored.

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Homework Statement



Suppose that f(x)>=0 in some deleted neighborhood of c, and that lim x->a f(x)=R. Prove that lim x->a sqrt{f(x)}=sqrt{R} under the assumption that R>0.

Homework Equations



if 0<|x-c|<delta, then |f(x)-L|<epsilon.

The Attempt at a Solution



I don't know how to start with this.

I tried to work on lsqrt{f(x)}-sqrt(L)l=lsqrt{f(x)}-sqrt(L)llsqrt{f(x)}+sqrt(L)l/lsqrt{f(x)}+sqrt(L)l
=lsqrt{f(x)}-sqrt(L)l/(sqrt{f(x)}+sqrt(L))

But I don't know how to go from here, I'm not sure if it's a correct start as well.

Any help would be appreciated. Thanks!
 
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No, you calculated wrong. What is

\frac{|\sqrt{f(x)}-\sqrt{L}||\sqrt{f(x)}+\sqrt{L}|}{ |\sqrt{f(x)}+\sqrt{L}|}
 
I actually don't know what it is...I just don't know how to proceed. Could you help me how I get to start with this question?
 
You have a deleted neighborhood of c, so isn't this lim x ➙ c , not lim x ➙ a ?
 
Yes, you're right.
 
Since f(x) > 0, R>0, Hence 0 < |√(f(x)) - √(R)| < |√(f(x)) + √(R)|.

for ε^2 given there exists δ>0 such that when |x-c| <δ, |f(x) - R| < ε^2.

then

|√(f(x)) - √(R)|^2 < |√(f(x)) - √(R)||√(f(x)) + √(R)| = |f(x) - R| < ε^2,

taking square roots give the desired result.
 
Thank you for your help. But, sorry, how can I conclude this? Why can I say that lim x->a sqrt{f(x)}=sqrt{R}?
 
(a - b)(a + b) = a2 - b2 .

What is |\sqrt{f(x)}-\sqrt{L}||\sqrt{f(x)}+\sqrt{L}|\,?

Now can you answer micromass's question?
 
SammyS

Sorry, which part you're asking? Is it for what Trevor Vadas said?

I'm now just wondering how I can conclude this problem from |√(f(x)) - √(R)|^2 < |√(f(x)) - √(R)||√(f(x)) + √(R)| = |f(x) - R| < ε^2.
 

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