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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 x2 − 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.