Algebraically closed extension in the context of "Absolutely irreducible"

In mathematics, a zero (also sometimes called a root) of a real-, complex-, or generally vector-valued function ${\displaystyle f}$, is a member ${\displaystyle x}$ of the domain of ${\displaystyle f}$ such that ${\displaystyle f(x)}$ vanishes at ${\displaystyle x}$; that is, the function ${\displaystyle f}$ attains the value of 0 at ${\displaystyle x}$, or equivalently, ${\displaystyle x}$ is a solution to the equation ${\displaystyle f(x)=0}$. A "zero" of a function is thus an input value that produces an output of 0.

A root of a polynomial is a zero of the corresponding polynomial function. The fundamental theorem of algebra shows that any non-zero polynomial has a number of roots at most equal to its degree, and that the number of roots and the degree are equal when one considers the complex roots (or more generally, the roots in an algebraically closed extension) counted with their multiplicities. For example, the polynomial ${\displaystyle f}$ of degree two, defined by ${\displaystyle f(x)=x^{2}-5x+6=(x-2)(x-3)}$ has the two roots (or zeros) that are 2 and 3.$${\displaystyle f(2)=2^{2}-5\times 2+6=0{\text{ and }}f(3)=3^{2}-5\times 3+6=0.}$$