Show the limit exists or does not exist

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  • #1
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Homework Statement


c2f1f923-74de-46af-bb68-3ccd4efeb33a.jpe


The Attempt at a Solution


it does not exist, but i cant get different limits, im only getting it approaches 0

i replaced x=1 only, y=0 only, y=x, x=y but i'm only getting 0 as my limit.

thanks
 
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Answers and Replies

  • #2
mathwonk
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this is a trick. notice it is equivalent to finding the limit of [xy]/(x^2+y^2) as (x,y)-->(0,0).

this one is very familiar, and is done by letting x=y.
 
  • #3
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im still approaching 0 when x=y
 
  • #4
gb7nash
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im still approaching 0 when x=y
You shouldn't be. Replacing y with x:

[tex]\lim_{(x,y) \to (0,0)} \frac{x*x}{x^2+x^2} = ...[/tex]
 
  • #5
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oh so first i rewrite the limit into a more familiar one and then solve. but i don't see how they are related.

edit:nvm i got it.
 
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  • #6
SammyS
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Homework Statement


c2f1f923-74de-46af-bb68-3ccd4efeb33a.jpe


The Attempt at a Solution


it does not exist, but i cant get different limits, im only getting it approaches 0

i replaced x=1 only, y=0 only, y=x, x=y but i'm only getting 0 as my limit.

thanks
Yes, if you let x=1, and take the limit of the result as y→0, the limit is zero.

Similarly, letting y=0 and taking the limit of the result as x→1, also gives zero.

Use these results along with the limit obtained as others have suggested. What's your final conclusion?
 
  • #7
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Yes, if you let x=1, and take the limit of the result as y→0, the limit is zero.

Similarly, letting y=0 and taking the limit of the result as x→1, also gives zero.

Use these results along with the limit obtained as others have suggested. What's your final conclusion?
i showed the relation between the original limit and [xy]/(x^2+y^2) as (x,y)-->(0,0).
numerator factorizes to y(x-1), then i replaced (x-1) with t, and as x→1, t→0. new limit does not exist because it approaches 1/2 and 0.
 
  • #8
SammyS
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Correct !
 

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