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" − 1, then the zeroes of the function are +1 and −1, because "f"(+1) = (+1) − 1 = 0, and "f"(−1) = (−1) − 1 = 0.