Prove by Beta and Sigma limit definition

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Discussion Overview

The discussion revolves around proving a limit using the beta and sigma definition, specifically for the limit of the expression (x+y)/(x^2+y^2) as (x,y) approaches (0,0). The scope includes mathematical reasoning and exploration of limit definitions in multivariable calculus.

Discussion Character

  • Exploratory
  • Mathematical reasoning

Main Points Raised

  • One participant requests help in proving a limit using the beta and sigma definition.
  • Another participant questions what the beta and sigma definitions are, suggesting they may be analogous to the epsilon and delta definitions.
  • A different participant expresses uncertainty about the beta/sigma definitions and asks for clarification.
  • One participant proposes that to prove the limit, one must show that for a given beta > 0, a corresponding sigma > 0 can be found such that if the distance from the origin (x,y) is less than sigma, then the expression (x+y)/(x^2+y^2) is less than beta.
  • This participant suggests using the inequality x+y ≤ (x^2+y^2)^2 in conjunction with the condition on sigma to define a function sigma(beta).

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus on the definitions of beta and sigma limits, and there is uncertainty regarding their relationship to epsilon and delta definitions. The discussion remains unresolved regarding the proof itself.

Contextual Notes

There are missing definitions and references for the beta and sigma limit concepts, which may affect the clarity of the discussion. The proposed approach relies on specific inequalities that have not been fully explored or validated.

kidia
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Please any help.

Use the symbols [tex]\beta[/tex] and [tex]\sigma[/tex] definition of limit to prove that limit (x,y)[tex]\Longrightarrow[/tex](0,0)x+y/x[tex]\x^2[/tex]+y[tex]\y^2[/tex]=0
 
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I think beta/sigma definitions are a 2D analogue to epsilon/deltas? I'm afraid I can't find any reference to them, you'll have to define them please.
 
You want to show that for a given [itex]\beta >0[/itex], you can find a number [itex]\sigma >0[/itex] such that when the distance from the origin of the point (x,y) is smaller than [itex]\sigma[/itex], then this implies that

[tex]\frac{x+y}{x^2+y^2}<\beta[/itex] <br /> <br /> So we kinda want to find a function [itex]\sigma(\beta)[/itex]. <br /> <br /> The statement "the distance from the origin of the point (x,y) is smaller than [itex]\sigma[/itex]" is written mathematically as [itex]\sqrt{x^2+y^2}<\sigma[/itex]<br /> <br /> There are many solutions but here's a hint based on one:<br /> <br /> Use the fact that [itex]x+y \leq (x^2+y^2)^2[/itex] coupled with the hypothesis [itex]\sqrt{x^2+y^2}<\sigma[/itex] to define a function [itex]\sigma(\beta)[/itex].[/tex]
 

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