Is There a Positive Constant for a Polynomial Inequality with Two Variables?

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Discussion Overview

The discussion centers on the existence of a positive constant C for a polynomial inequality involving two variables, specifically whether the inequality p(x,y) ≥ C (|x| + |y|)^n holds for all -1 ≤ x, y ≤ 1, given that p(x,y) is a polynomial of degree n that equals zero only at the origin.

Discussion Character

  • Exploratory
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant queries the meaning of the expression (|x| + |y|)^n, seeking clarification on the notation used.
  • Another participant explains that the expression refers to the sum of the absolute values of x and y raised to the nth power.
  • A participant suggests that since (0,0) is the only root of the polynomial, it implies that p(x,y) is greater than 0 elsewhere.
  • There is a proposal to analyze the structure of a 2D polynomial and its behavior within the bounds |x|, |y| ≤ 1.
  • One participant raises a question about the existence of the limit p(x,y)/(|x| + |y|)^n as (x,y) approaches (0,0), suggesting that this limit could provide a solution to the problem.
  • Another participant asks for clarification on what limit is being considered, specifically what values x and y are approaching.
  • A participant asserts that the limit will tend to zero due to the continuity of polynomials, indicating that the limit of p(x,y) as (x,y) approaches (0,0) will equal p(0,0) = 0.

Areas of Agreement / Disagreement

Participants express differing views on the implications of the polynomial's continuity and the behavior of the limit as (x,y) approaches (0,0). There is no consensus on whether the limit exists in a finite form or how it relates to the original inequality.

Contextual Notes

The discussion includes assumptions about the behavior of polynomials and their continuity, but these assumptions are not universally accepted among participants. The implications of the polynomial's structure and the conditions under which the inequality holds are also not fully resolved.

hedipaldi
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Hi
Let p(x,y)≥0 be a polynomial of degree n such that p(x,y)=0 only for x=y=0.Does there exist a positive constant C such that the inequality p(x,y)≥C (IxI+IyI)^n (strong inequality!) holds for all -1≤x,y≤1?
The simbol I I stands for absolute value.
 
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Hey hedipaldi.

What does (IxI + IyI)^n refer to? (what are the I's)?
 
Thise are absolute values.It means [abs.val(x)+abs.val(y)]^n
 
If (0,0) is the only root then it means that everything is greater than 0.

The only thing now is to consider the makeup of a 2D polynomial.

If the double polynomial (or bivariate polynomial) has a structure p(x,y) = (a_n*x^n + a_(n-1)*x^(n-1) + ... + a0)*(b_n*y^n + b_(n-1)*y^(n-1) + ... + b0) and consider the behaviour in the region |x|, |y| <= 1.
 
Does the limit p(x,y)/[absvalue(x)+absvalue(y)]^n nesecarily exist (finite or +infinite)?
This will solve my problem.
 
What limit are you thinking of? (In other words what does x and y tend to)?
 
x and y tend to o. i.e (x,y) tends to (0,0).
 
It will tend to zero because all polynomials (including bi-variate ones) are continuous.

Continuity implies that lim x->a, y->b f(x,y) = f(a,b) = 0 for (a=0,b=0).
 

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