Multivariable limit evaluation

In summary, the conversation is discussing how to approach the limit (x,y) --> (0,0) [sin(2x) -2x + y]/[x^3+y]. The person attempts to approach from the x-axis, y-axis, and a line y=x, but all result in the indeterminate form 0/0. They suggest using L'Hopital's Rule, but note that it only applies to single variable limits. Another person suggests approaching the limit along the curve y=mx^3. The conversation ends with the first person trying L'Hopital's Rule again but still getting 0/0.
  • #1
Kuma
134
0

Homework Statement




lim
(x,y) --> (0,0) [sin(2x) -2x + y]/[x^3+y]

Homework Equations





The Attempt at a Solution



so I tried approaching from the x-axis and I got

y=0 lim x-> 0 [sin(2x) -x + 0]/[x^3 + 0] which gives me 0/0

and from the y axis

y=0 lim y ->0 which gives me lim y-> 0 y/y = 0/0

if I try approaching from a line such as y = x I also get 0/0

what do I do now? L'hopitals rule? If so I'm not sure how to use it here...
 
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  • #2
I think you'll find that, for any line you choose to approach the origin with, you'll get a single variable limit of 0/0 form. You may apply L'Hospital's Rule for this. Remember that L'Hospital's Rule only works for single variable limits.

If you are having difficulty getting differing limits, try approaching the origin via the line,

[tex]y=mx[/tex]

It'll follow quite naturally from this.
 
  • #3
okay so then using l hopitals rule for this, since it only applies for single variable limits, if I choose y=0 and evaluate it at

lim x-> 0 I get sin(2x) - 2x/x^3 then using l hopitals rule which is

lim x->a f'(x)/g'(x) I get

2 cos(2x) -2/3x^2, evaluating that at x=0 I still get 0/0...

so what now?
 
  • #4
For (2 cos(2x) -2)/3x2 , use L'Hôpital's rule again, then again.
 
  • #5
Try approaching (0,0) along the curve, y = m(x3)
 

1. What is a multivariable limit?

A multivariable limit is a mathematical concept that describes the behavior of a function as it approaches a certain point in a multi-dimensional space. It is typically denoted as lim(x,y)→(a,b)f(x,y), where f(x,y) is the function and (a,b) is the point in question.

2. How do you evaluate a multivariable limit?

To evaluate a multivariable limit, you must first determine if the function is continuous at the point in question. If it is, then you can simply plug in the values of (a,b) into the function to find the limit. If the function is not continuous, then you will need to use more advanced techniques such as L'Hospital's rule or algebraic manipulation to evaluate the limit.

3. What is the difference between a multivariable limit and a single variable limit?

The main difference between a multivariable limit and a single variable limit is the number of dimensions involved. A single variable limit only considers the behavior of a function along a single axis, whereas a multivariable limit takes into account the behavior of a function along multiple axes in a multi-dimensional space.

4. Can a multivariable limit exist but not be equal to the value of the function at that point?

Yes, it is possible for a multivariable limit to exist but not be equal to the value of the function at that point. This typically occurs when the function is not continuous at the point in question, and the limit represents the behavior of the function as it approaches the point rather than the value at the point itself.

5. What are some real-world applications of multivariable limit evaluation?

Multivariable limit evaluation is commonly used in fields such as physics, engineering, and economics to model and analyze complex systems that involve multiple variables. It is also used in optimization problems to find the maximum or minimum value of a function in a multi-dimensional space.

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