Finding Limit of Multivariable Function

In summary, when finding the limit of a multivariable function, you do not use partial derivatives. Instead, you compare a few instances, such as x = 0, y = 0, and x = y, to determine if the limit exists. L'Hopital's rule cannot be used for multivariable limits. When both the numerator and denominator go to 0, you must substitute different values for x and y separately and not plug in actual numbers. It is important to note that plugging in actual numbers may give a false answer.
  • #1
ultra100
9
0
How do I go about finding the limit of a multivariable function? Example:

limit as (x,y) approach (0,0) of:

(x + 2y) / sqrt (x^2 + 4(y^2))



Do I need to use partial derivatives?
 
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  • #2
No. When dealing with multivariable limits you do not find their partial derivatives. Instead, you take a few instances and compare the results to each other. Such as x = 0, y = 0, x= y. If none of them match, then you can be certain that the limit does not exist.
 
  • #3
jheld said:
No. When dealing with multivariable limits you do not find their partial derivatives. Instead, you take a few instances and compare the results to each other. Such as x = 0, y = 0, x= y. If none of them match, then you can be certain that the limit does not exist.


What about when the numerator and denominator both go to 0, so you get 0/0?

I tried plugging in small numbers like 0.1 and 0.01 for x and y and i get 3/sqrt(5) as the answer, but my book says the limit does not exist for this equation

Is there a way to do L'Hospitals on multivariable limits?
 
  • #4
No, unfortunately you can't use L'Hospitals for mutlivars. When both num and denom go to 0, that means that you need to substitute in y and x in different ways, like x = 0 in one case, and then y = 0 in another case, and then x = y in another. don't do them at the same time. don't plug in actual numbers (other than 0), only stuff like I noted above.
 

FAQ: Finding Limit of Multivariable Function

What is the definition of a limit of a multivariable function?

The limit of a multivariable function is the value that a function approaches as the input variables approach a certain point, also known as the limit point. It represents the behavior of the function at that particular point.

Can a multivariable function have more than one limit?

Yes, a multivariable function can have multiple limits depending on the approach of the input variables towards the limit point. If the function approaches different values from different directions, then it has multiple limits.

How do you find the limit of a multivariable function algebraically?

To find the limit of a multivariable function algebraically, you can use the same methods as for single-variable functions, such as substitution and factoring. You can also use the squeeze theorem and L'Hopital's rule in certain cases.

What is the significance of finding the limit of a multivariable function?

Finding the limit of a multivariable function is important in understanding the behavior of the function at a particular point. It helps in determining the continuity and differentiability of the function, and also in solving optimization problems in calculus.

Are there any limitations to finding the limit of a multivariable function?

Yes, there are certain limitations to finding the limit of a multivariable function. It may not exist if the function has a discontinuity at the limit point or if it approaches different values from different directions. The limit may also be undefined if the function approaches infinity or oscillates infinitely at the limit point.

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