Solving a Limits Question in Schaum's: Uncovering the Answer of 1/(2*sqrt(3))

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Discussion Overview

The discussion revolves around a limits question from Schaum's that involves evaluating the limit of a function as x approaches 0. The specific limit in question is presented as lim(x>0) ((sqrt(x+3))-(sqrt(3))/x, with the expected answer being 1/(2*sqrt(3)). Participants explore methods for simplifying the expression to resolve the limit.

Discussion Character

  • Homework-related
  • Mathematical reasoning

Main Points Raised

  • One participant expresses confusion about simplifying the limit expression and initially believes it has no limit.
  • Another participant suggests multiplying by the conjugate to simplify the expression, explaining that this technique is often useful in such cases.
  • A participant requests a definition of the term "conjugate," indicating a desire for clarification on the concept.
  • A further explanation is provided regarding the meaning of "conjugate" in the context of square roots, emphasizing its role in rationalizing expressions.
  • One participant notes that the limit can be recognized as the definition of the derivative of the square root function evaluated at 3, although this is presented as a side note rather than a central focus of the discussion.
  • A participant acknowledges their current level of understanding regarding limits and expresses intent to learn about derivatives in the future.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the best approach to simplify the limit, and there are varying levels of understanding regarding the concept of conjugates and their application in this context.

Contextual Notes

Some participants exhibit uncertainty about the application of the conjugate method and its effectiveness in resolving the limit. There is also a lack of clarity on the definitions and implications of terms used in the discussion.

Who May Find This Useful

This discussion may be useful for students learning about limits and derivatives, particularly those seeking clarification on techniques for evaluating limits involving square roots.

eprjenkins
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I have been reading through Schaum's and came across a limits question that i cannot figure out. I thought it had no limit but the answer is 1/(2*sqrt(3)). I have no idea of how to use latex so I will attempt it using basic characters; hopefully not to obscure.

lim(x>0) ((sqrt(x+3))-(sqrt(3))/x

I cannot see how to simplify in order to get rid of the denominator x.
 
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Multiply the whole thing by (sqrt(x+3)+sqrt(3))/(sqrt(x+3)+sqrt(3)). This is called multiplying by the conjugate and its often useful. The effect is to "switch" the square roots from denom to num. (or vice versa) and to take the arguments of the square roots "out of them". Understandable?
 
Merci beaucoup, all is clear. If not too difficult can you give me a definition of the conjugate? Maybe its in this book...
 
eprjenkins said:
Merci beaucoup, all is clear. If not too difficult can you give me a definition of the conjugate? Maybe its in this book...

"conjugate" may mean several things. But in this particular case, say, we have the expression: [tex]\sqrt{a} + \sqrt{b}[/tex], then its conjugate is: [tex]\sqrt{a} - \sqrt{b}[/tex], or [tex]\sqrt{b} - \sqrt{a}[/tex].

This is a common practice in taking the limit of something, especially in the form 0 / 0. Since you can factor a polynomial, but not a surd. So, what you should do is to rationalize it, i.e eliminate the square roots.
 
This is some circular logic here but in case you just wanted to value and not how to prove it, you could recognize that the limit you stated is the definition for the derivative of the square root function evaluated at 3.
 
Thank you all. Gib Z, I have only begun limits; but I'm sure I'll get to derivatives and the like soon, only a few chapters away.
 

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