(open) Boundaries on the roots of splitting real polynomials

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SUMMARY

The discussion focuses on the boundaries of the roots of real polynomials, specifically the polynomial of the form ##x^n + a_{n−1}x^{n−1} + \cdots + a_0##. It establishes that if all roots are real, they are contained within the interval defined by the endpoints $$-\dfrac{a_{n-1}}{n} \pm \dfrac{n-1}{n}\sqrt{a_{n-1}^2 - \dfrac{2n}{n-1}a_{n-2}}$$. The Cauchy-Schwarz inequality serves as a crucial tool in deriving this result. For the case of n=2, the formula aligns with the well-known quadratic equation solution.

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  • Familiarity with the Cauchy-Schwarz inequality
  • Knowledge of quadratic equations and their solutions
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  • Study the application of the Cauchy-Schwarz inequality in polynomial root analysis
  • Explore the implications of the derived root boundaries for higher-degree polynomials
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Mathematicians, students studying algebra, and researchers interested in polynomial theory and root analysis will benefit from this discussion.

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Suppose all roots of the polynomial ##x^n+a_{n−1}x^{n−1}+\cdots+a_0## are real. Then the roots are contained in the interval with the endpoints
$$
-\dfrac{a_{n-1}}{n} \pm \dfrac{n-1}{n}\sqrt{a_{n-1}^2-\dfrac{2n}{n-1}a_{n-2}}\,.
$$
Hint: Use the inequality of Cauchy-Schwarz.
 
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For n=2 the formula is familiar quadric equation solution. :smile:
 
anuttarasammyak said:
For n=2 the formula is familiar quadric equation solution. :smile:
... and this observation is one hint to the proof!
 

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