If negative 1 is a root of f of x , which of the following must be true?

If −1 is a root, then f(−1) = 0. By the Factor Theorem, (x − r) is a factor when r is a root; substituting r = −1 gives x − (−1) = x + 1. Therefore, (x + 1) must be a factor of f(x).

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