functions are explained in the function (mathematics) article. if the function "f"("x") = 0, then "x" is called a zero (or root) of the function "f". for example, if the function "f"("x") is "x"2 − 1, then the zeroes of the function are +1 and −1, because "f"(+1) = (+1)2 − 1 = 0, and "f"(−1) = (−1)2 − 1 = 0.