Solving Multi-Limits: x to 0, y to 0

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In summary, the limit of (xyln(x^2+y^2)) as x and y approach 0 does not exist. This is shown by converting to polar coordinates and letting r approach 0, which gives a limit of 0. Using a different path, y=1/x, is not valid as it does not approach (0,0).
  • #1
supercali
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Homework Statement


solve
[tex] {\lim }\limits_{\scriptstyle x \to 0 \hfill \atop
\scriptstyle y \to 0 \hfill} (xy\ln \left( {x^2 + y^2 } \right)) [/tex]

Homework Equations


[tex]y_{1}=x[/tex]
[tex]y_2=1/x[/tex]

The Attempt at a Solution


when using [tex]y_{1}=x[/tex] we get that the limit is zero
when using this [tex]y_{2}=1/x[/tex] we get that the limit is infinity
thus the limit does not ! exist.
i don't know if it is ok to use these 2 paths i some how have a feeling that the second one is wrong
thanks for the help
 
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  • #2
Convert it to polar and let r->0. You get that the limit is zero. Also, the whole idea of using a path is to show the limits do not exist by showing that if you approach the point 0,0 along different paths then you get different limits. y = 1/x never approaches (0,0)
 

What is the concept of solving multi-limits?

Solving multi-limits involves finding the limit of a function as two or more variables approach certain values simultaneously.

What is the importance of solving multi-limits?

Solving multi-limits allows us to understand the behavior of a function near a certain point and make predictions about its value. It is also a fundamental concept in calculus and is used in many real-world applications.

What are the common techniques used to solve multi-limits?

The most common techniques include substitution, factoring, and using limit laws such as the sum, product, and quotient rules. L'Hopital's rule and Taylor series expansion can also be used in more complex cases.

How do you determine if a multi-limit exists?

If the limit of a function approaches the same value regardless of which path the variables approach the point, then the limit exists. This can be determined by evaluating the limit from different directions or using the Squeeze Theorem.

What are some common mistakes to avoid when solving multi-limits?

Some common mistakes include assuming that limits can be simplified like regular algebraic expressions, not considering all possible paths of approach, and forgetting to check for indeterminate forms such as 0/0 or infinity/infinity. It is also important to carefully apply limit laws and understand the properties of the functions involved.

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