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Difference between revisions of "Vieta's Formulas"

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== Related Links ==
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[http://mathworld.wolfram.com/VietasFormulas.html Mathworld's Article]

Revision as of 00:26, 19 June 2006

Background

Let $P(x)={a_n}x^n+{a_{n-1}}x^{n-1}+\cdots+{a_1}x+a_0$, where the coefficient of $x^{i}$ is ${a}_i$. As a consequence of the Fundamental Theorem of Algebra, we can also write $P(x)=a_n(x-r_1)(x-r_2)\cdots(x-r_n)$, where ${r}_i$ are the roots of $P(x)$.

Also, let ${\sigma}_k$ be the ${}{k}$th symmetric sum.

Statement

$\sigma_k = (-1)^k\cdot \frac{a_{n-k}}{a_n{}}$, for ${}1\le k\le {n}$.

Proof

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Related Links

Mathworld's Article

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