Proving Continuity of a Multivariable Function Using Inequalities

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SUMMARY

The discussion focuses on proving the continuity of the multivariable function defined as f(0,0)=0 and f(x,y) = (x² + y² - 2x²y - 4x⁶y²)/(x⁴ + y²)². Participants confirm that the inequality 4x⁴y² ≤ (x⁴ + y²)² holds true, which is essential for establishing continuity. The critical step involves demonstrating that the limit of the problematic term, 4x⁶y²/(x⁴ + y²)², approaches zero as (x,y) approaches (0,0), thereby confirming the function's continuity at the origin.

PREREQUISITES
  • Understanding of multivariable calculus concepts, specifically limits and continuity.
  • Familiarity with inequalities and their applications in mathematical proofs.
  • Knowledge of the behavior of rational functions as variables approach specific values.
  • Experience with limit evaluation techniques in multivariable contexts.
NEXT STEPS
  • Study the epsilon-delta definition of continuity in multivariable functions.
  • Learn about the Squeeze Theorem and its application in proving limits.
  • Explore examples of continuity proofs for rational functions in multiple variables.
  • Investigate the implications of continuity on differentiability in multivariable calculus.
USEFUL FOR

Students and educators in multivariable calculus, mathematicians focusing on continuity proofs, and anyone interested in the application of inequalities in mathematical analysis.

Maraduke
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Homework Statement


Define f(0,0)=0 and f(x,y) = x2 +y2-2x2y-4x6y2/(x4+y2)2.

Show for all (x,y) that 4x4y2<=(x4+y2)2 and conclude that f is continuous.


Homework Equations





The Attempt at a Solution


Showing the inequality is trivial, but I do not see how I can conclude the function is continuous. I've done some messing around with the form of f, but am not getting anywhere.
 
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The only term that can cause a problem is the last one:

[tex]\frac{4x^6y^2}{(x^4+y^2)^2}[/tex]

Since you have set the function equal to 0 at the origin, the following must be true in order to have continuity:

[tex]\lim_{x,y \rightarrow 0}\frac{4x^6y^2}{(x^4+y^2)^2} = 0[/tex]

Which part of this fraction has a [itex]4x^4y^2[/itex] in it? That's the logical place to try using the hint.
 

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