Two Path Test

  1. Feb 27, 2012 #1
    1. The problem statement, all variables and given/known data
    Use the two path test to prove that the following limits do not exist.


    2. Relevant equations

    [tex]\lim_{(x,y)\rightarrow{(0,0)}}\frac{4xy}{3x^2+y^2}[/tex]



    3. The attempt at a solution
    The book that I am using introduces the Two Path Test theoretically but does not show an example of how to do it, so I am a bit lost.

    Would I set x = y, and x = -y? In some of the more basic problems I was able to set x = 0 and y = 0, and find the limits would differ, proving that there was no limit. But in this case, that's obviously not possible.
     
  2. jcsd
  3. Feb 27, 2012 #2

    Dick

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    Those two paths look like a good choice to me. Try them out. What's the limit along each path?
     
  4. Feb 27, 2012 #3
    I'm getting 1 and -1, thus the limit does not exist. A question that I have that the book does not address: how do I choose the paths? Do you just try what you think will work until you find something, or is there a specific method of choosing?
     
  5. Feb 27, 2012 #4

    Dick

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    There's no formula for picking the paths. Just try some until you get a feeling for what's going on. Other easy ones to try are x=0 and y=0.
     
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