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MATH
[1251]

Definitions from Complex polynomials

All definitions from Complex polynomials.

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Complex polynomial

A complex polynomial is a function p:C→Cp:\mathbb C\to\mathbb C of the form

p(z)=a0+a1z+a2z2+⋯+anzn,a0,…,an∈C,p(z)=a_0+a_1z+a_2z^2+\cdots+a_nz^n, \qquad a_0,\ldots,a_n\in\mathbb C,

for a non-negative integer nn.

The coefficients may be real or non-real. The word polynomial restricts the exponents of the variable to non-negative integers, not the kinds of numbers allowed as coefficients.

Degree

For a non-zero polynomial

p(z)=∑k=0nakzk,p(z)=\sum_{k=0}^n a_kz^k,

the degree of pp is the largest integer kk for which ak≠0a_k\ne0. The zero polynomial has undefined degree.

Polynomial root

A number α∈C\alpha\in\mathbb C is a root of pp if

p(α)=0.p(\alpha)=0.

Polynomial factor

A polynomial p1p_1 is a factor of pp if there is a polynomial p2p_2 such that

p(z)=p1(z)p2(z)p(z)=p_1(z)p_2(z)

for every z∈Cz\in\mathbb C.

Root multiplicity

For a non-zero polynomial pp, a root α\alpha has multiplicity k≥1k\ge1 if (z−α)k(z-\alpha)^k is a factor of pp but (z−α)k+1(z-\alpha)^{k+1} is not.

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