Limit of a two-variable function

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Homework Help Overview

The discussion revolves around the limit of a two-variable function as it approaches the origin, specifically evaluating the limit of the expression ##\displaystyle \lim_{(x,y) \rightarrow (0,0)} = \frac{\sqrt{x^2+y^2+xy^2}}{\sqrt{x^2+y^2}}##. Participants are exploring whether this limit exists and under what conditions.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants are attempting to evaluate the limit along various curves, such as y=x, y=0, and y=x^2, and consistently find a limit of 1. However, there are questions about whether this is sufficient to prove the limit exists universally. Some suggest converting to polar coordinates as a potential method for further evaluation.

Discussion Status

The discussion is ongoing, with participants providing different approaches to the problem. There is a suggestion that converting to polar form may help clarify the limit's behavior, although some participants express uncertainty about the next steps in this approach. There is no explicit consensus on the existence of the limit yet.

Contextual Notes

Participants note that evaluating the limit along multiple curves may not be sufficient to establish its existence, indicating a need for a more rigorous proof. There are also indications of confusion regarding the expressions used in polar coordinates.

Mr Davis 97
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Homework Statement


Does the following limit exist: ##\displaystyle \lim_{(x,y) \rightarrow (0,0)} = \frac{\sqrt{x^2+y^2+xy^2}}{\sqrt{x^2+y^2}}##?

Homework Equations

The Attempt at a Solution


So I am trying to evaluate the limit along several curves, such as y=x, y=0, y=x^2, and I keep getting 1. I can't think of any other curves to evaluate on. Does the limit exist or is there another curve that I am not evaluating that gives a different limit?
 
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Mr Davis 97 said:
So I am trying to evaluate the limit along several curves, such as y=x, y=0, y=x^2, and I keep getting 1
If it does exist, it does not matter how many curves you try you will not have proved it. So how about trying to prove it exists?
 
Mr Davis 97 said:

Homework Statement


Does the following limit exist: ##\displaystyle \lim_{(x,y) \rightarrow (0,0)} = \frac{\sqrt{x^2+y^2+xy^2}}{\sqrt{x^2+y^2}}##?

Homework Equations

The Attempt at a Solution


So I am trying to evaluate the limit along several curves, such as y=x, y=0, y=x^2, and I keep getting 1. I can't think of any other curves to evaluate on. Does the limit exist or is there another curve that I am not evaluating that gives a different limit?
Converting to polar form is fruitful, showing that the limit does exist.
 
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Mark44 said:
Converting to polar form is fruitful, showing that the limit does exist.
Converting to polar form, I get, after simplification, ##\displaystyle \lim_{r \rightarrow 0^+} \sqrt{1+\cos \theta \sin^2 \theta}##. I'm not sure how to proceed
 
Mr Davis 97 said:
Converting to polar form, I get, after simplification, ##\displaystyle \lim_{r \rightarrow 0^+} \sqrt{1+\cos \theta \sin^2 \theta}##. I'm not sure how to proceed
You seem to have dropped an r.
 
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Mr Davis 97 said:
Converting to polar form, I get, after simplification, ##\displaystyle \lim_{r \rightarrow 0^+} \sqrt{1+\cos \theta \sin^2 \theta}##. I'm not sure how to proceed

Wrong expression!
 

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