Root of a function

In mathematics, a root of a function f is a number x that turns the value of f to 0:

f(x) = 0.

Because polynomials are also functions, roots are real things.

The fundamental theorem of algebra says every polynomial with complex coefficients has at least one (complex) root. Using the fundamental theorem of algebra and the polynomial remainder theorem together shows that every complex polynomial of degree n has exactly n complex roots, and some of them may be equal.