How Can f and g Be Expressed Using Elementary Symmetric Polynomials?

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Discussion Overview

The discussion revolves around expressing the polynomials f and g, defined as f = x^8 + y^8 + z^6 and g = x^3 + y^3 + z^3, in terms of elementary symmetric polynomials in the variables x, y, and z. The context includes theoretical exploration and mathematical reasoning regarding the applicability of Newton's formulas and the properties of symmetric polynomials.

Discussion Character

  • Exploratory
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant notes that g can be expressed using Newton's formula, while f is not symmetric.
  • Another participant provides a formulation for g using Newton's formula, questioning the correctness of their approach.
  • Concerns are raised about the inability to express f in terms of elementary symmetric polynomials, with a specific argument that f does not conform to the required form for such expressions.
  • A further argument is presented that if f were expressible in terms of elementary symmetric polynomials, it would lead to a contradiction when switching variables y and z, indicating that f cannot be expressed in that manner.

Areas of Agreement / Disagreement

Participants generally agree that g can be expressed using Newton's formula, while there is disagreement and uncertainty regarding the expressibility of f in terms of elementary symmetric polynomials. The discussion remains unresolved regarding the precise conditions under which f cannot be expressed in that form.

Contextual Notes

Participants express uncertainty about the conditions that would definitively prove the impossibility of expressing f in terms of elementary symmetric polynomials. There is also a reliance on the properties of symmetric polynomials and the implications of variable switching.

math_grl
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Let [tex]f, g \in \mathbb{Z}[x, y, z][/tex] be given as follows: [tex]f = x^8 + y^8 + z^6[/tex] and [tex]g = x^3 +y^3 + z^3[/tex]. Express if possible [tex]f[/tex] and [tex]g[/tex] as a polynomial in elementary symmetric polynomials in [tex]x, y, z[/tex].

Professor claims there is an algorithm we were supposed to know for this question on the midterm. I missed it. Any ideas?
 
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g can be expressed as required using Newton's formula ; f is not even symmetric.
 
By Newton's formula,
[tex]g = (\sigma_1^2 - 2\sigma_2)\sigma_1 - \sigma_1 \sigma_2 + 3\sigma_3 = \sigma_1^2 - 3\sigma_1 \sigma_2 + 3\sigma_3[/tex]

where the [tex]\sigma_i[/tex]'s are the elementary symmetric polynomials?

just trying to verify that I did it right?

and f is not of the form [tex]\sum^n_{i=1} x_i^k[/tex] for some [tex]k \in \mathbb{N}[/tex] so we can't use Newton's formula...but I was wondering one would know precisely that it's not possible to express it in terms of the e.s.p.'s?
 
math_grl said:
and f is not of the form [tex]\sum^n_{i=1} x_i^k[/tex] for some [tex]k \in \mathbb{N}[/tex] so we can't use Newton's formula...but I was wondering one would know precisely that it's not possible to express it in terms of the e.s.p.'s?

Suppose that f = P(s1,s2,...) is expressible in terms of the e.s.p.'s. P won't change on switching y & z ; f will. A contradiction.
 

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