Two Path Test


by mharten1
Tags: path, test
mharten1
mharten1 is offline
#1
Feb27-12, 03:48 PM
P: 63
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.
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Dick
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Feb27-12, 03:51 PM
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Those two paths look like a good choice to me. Try them out. What's the limit along each path?
mharten1
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Feb27-12, 03:54 PM
P: 63
Quote Quote by Dick View Post
Those two paths look like a good choice to me. Try them out. What's the limit along each path?
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?

Dick
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Feb27-12, 04:06 PM
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Two Path Test


Quote Quote by mharten1 View Post
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?
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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