数学上，函数的一个根（或称零点）是的定义域中适合的元素。

例子：

• 若是实数域上定义的函数，它的根是所有形如的数（为整数）。
• 若是实数域上定义的函数，它的根是。若的定义域扩展至复数，则它会多了两个根。

In mathematics, a zero, also sometimes called a root, of a real-, complex- or generally vector-valued function f is a member x of the domain of f such that f(x) vanishes at x; that is, x is a solution of the equation

In other words, a "zero" of a function is an input value that produces an output of zero (0).