Multivariable limits - path problem

Click For Summary

Discussion Overview

The discussion revolves around the problem of determining the existence of a limit in a multivariable context. Participants explore various paths and approaches to analyze the limit, including specific substitutions and factorizations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant proposes to prove that the limit does not exist by examining the limit along the path defined by \(y=mx\) and suggests using \(x=\sin(y)\) to explore the behavior of the limit.
  • Another participant challenges the use of the path \(y=mx\), stating it is inconsistent with the conditions \(y \to 0\) and \(x \to 1\), and recommends trying \(y=m(x-1)\) instead.
  • A third participant suggests factoring the denominator as \((x-1)(x+3)\) to aid in the analysis of the limit.
  • A later reply discusses the behavior of \(y\) values constrained to \(-1

Areas of Agreement / Disagreement

Participants express differing views on the appropriate paths to analyze the limit, indicating that there is no consensus on the method to determine the limit's existence.

Contextual Notes

Some assumptions about the paths and their consistency with the limit conditions are not fully resolved, and there are indications of potential errors in earlier claims regarding the values to which \(x\) approaches.

WonderKitten
Messages
4
Reaction score
1
TL;DR
What path could I use to prove that the following limit doesn't exist.
Hey, so I have the following problem:
1605213504734.png

I'm trying to prove that the limit doesn't exist (although I'm not sure if it does or not) so:
along y=mx -> x=y/m:
1605213873389.png
, which is 0 for all k≠0.
along y^n it's the same and I'm not sure what I should do next. Could I set x = sin(y)?
If I can, then the limit in that instance would be infinite, thus proving that the limit doesn't exist, right?
 
  • Like
Likes   Reactions: Delta2
Physics news on Phys.org
You cannot use ##y=mx## since it is inconsistent with ##y\to 0## and ##x\to 1##. You might try ##y=m(x-1)##.
 
  • Like
Likes   Reactions: WonderKitten and Delta2
I also suggest along @mathman advice to factorize the denominator as ##(x-1)(x+3)##.
 
  • Like
Likes   Reactions: WonderKitten
You know that for ##y## restricted to ##-1<y<1## and ##x## sufficiently near 1 (edited, was 0, which is wrong), there are values of ##y## where ##\sin(y) = x^2+2x-3## and other values for ##y## where ##\sin(y) = 2(x^2+2x-3)##. Those ##y## values go to zero as ##x## goes to 1 and give two different constant values, 1 and 2, for the ratio.

EDIT: I had x going to the wrong value, 0, when it should have been going to 1.
 
Last edited:
  • Like
Likes   Reactions: WonderKitten

Similar threads

  • · Replies 3 ·
Replies
3
Views
5K
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 21 ·
Replies
21
Views
6K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 15 ·
Replies
15
Views
2K
  • · Replies 9 ·
Replies
9
Views
4K
Replies
11
Views
2K
  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 5 ·
Replies
5
Views
2K