Solving limit with three variables

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Homework Help Overview

The discussion revolves around evaluating the limit of a function involving three variables as they approach zero. The specific limit in question is \(\lim_{(x,y,z) \to (0,0,0)} \frac {x^3 + y^3 + z^3} {x^2 + y^2 + z^2}\), which falls under the subject area of multivariable calculus.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants explore the behavior of the limit by substituting \(x^2+y^2+z^2=r^2\) and discussing the implications of this substitution as the variables approach zero. Questions arise regarding how the numerator behaves in relation to the denominator as the limit is evaluated.

Discussion Status

The discussion is ongoing, with participants examining different aspects of the limit. Some guidance has been offered regarding the relationship between the numerator and denominator, but there is no explicit consensus on the limit's value yet.

Contextual Notes

Participants are considering the implications of the variables approaching zero and the relationships between their magnitudes. There is an emphasis on understanding the behavior of both the numerator and denominator in the limit expression.

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Homework Statement



\lim_{(x,y,z) \to (0,0,0)} \frac {x^3 + y^3 + z^3} {x^2 + y^2 + z^2}

Homework Equations


The Attempt at a Solution



I believe the limit is going to 0, but I have yet to find a way to prove this is the case.
 
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Let x^2+y^2+z^2=r^2. Then as (x,y,z)->(0,0,0), r->0. But e.g. |x|<r. Do you see what I'm saying?
 
Dick said:
Let x^2+y^2+z^2=r^2. Then as (x,y,z)->(0,0,0), r->0. But e.g. |x|<r. Do you see what I'm saying?

Not quite. I understand what you are doing with the bottom, the equation is that of a sphere, and therefore you are using another equation to show the bottom is going to 0. But how exactly does that prove the numerator is going to 0 as well?
 
If |x|<r and |y|<r and |z|<r, what about |x^3+y^3+z^3|?
 

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