Can a finite polynomial have no roots on the left of the complex plane?

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Discussion Overview

The discussion revolves around the question of whether a finite polynomial can have no roots in the left half of the complex plane, specifically defined by the condition Re(x) < 0. Participants explore the implications of polynomial coefficients and potential mathematical theorems related to root locations.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant inquires about the existence of a theorem that guarantees a polynomial has no roots in the left half of the complex plane.
  • Another participant questions the restrictions on the polynomial's coefficients, providing a counterexample with a linear polynomial that has a root at x = -1.
  • A third participant suggests that the inquiry is about the conditions under which a polynomial can avoid roots with a negative real part.
  • A later reply proposes using a conformal map to transform the left half of the complex plane into the unit disk and suggests counting the zeros through an integral involving the derivative of the polynomial.

Areas of Agreement / Disagreement

Participants express differing interpretations of the original question, with some focusing on the conditions for roots while others provide counterexamples. The discussion remains unresolved regarding the existence of a general theorem applicable to the question posed.

Contextual Notes

There are limitations regarding the assumptions about the coefficients of the polynomial and the specific conditions under which the roots are being considered. The discussion does not clarify these assumptions fully.

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given a finite polynomial

[tex]a_{0}+a_{1}x+a_{2}x^{2}+a_{3}x^{3}+...+a_{n}x^{n} =P(x)[/tex]

is there a theorem or similar to ensure that P(x) has NO roots on the left of complex plane defined by [tex]Re(x<0)[/tex] ??
 
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What restrictions do you put on coefficients?

If you put n = 1, a_0 = 1, a_1 = 1, you get a polynomial with a root x=-1 on the left of complex plane right away. Perhaps I did not understand your question?
 
I think he's asking what conditions make it so there are no roots with real part negative
 
Ah! That makes sense.
 
Map the left of the complex plane to the unit disk via a conformal map (you need the möbius map) and then count the zeroes by evaluating the integral of f'/f.
 

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