Which of the following represents the factored form of f(x) = x3 − 81x?
f(x) = x(x − 9)2
f(x) = (x + 9)(x − 9)
f(x) = x(x + 9)(x − 9)
f(x) = x(x2 − 9)
f(x) = x(x − 9)2
f(x) = (x + 9)(x − 9)
f(x) = x(x + 9)(x − 9)
f(x) = x(x2 − 9)