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.

Step-by-step explanation: