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

A factor of f (x) is (x - 1).

A factor of f (x) is (x + 1).

Both (x - 1) and (x + 1) are factors of f (x).

Neither (x - 1) nor (x + 1) is a factor of f (x).

The correct answer is that a factor of f (x) is (x+1)

This is due to the zero product property, which states that if two binomials multiply to 0, then one of its factors must equal 0.

(x+1) must equal 0.

(x+1) = 0

x=-1

If (x-1) = 0, then x would equal 1 instead of - 1 which is what the question is asking for.