Root of a function
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In mathematics, a root of a function f is a number x that turns the value of f to 0:
f(x) = 0.
One can talk about polynomial roots, because a polynomial is also a function. There exists a theorem that states that every polynomial with complex coefficients has at least one (complex) root. From this and the polynomial remainder theorem it can be concluded that every complex polynomial of degree n has exactly n complex roots (some of them may be equal).