Select the factors of x^2 - 12x + 36.
(x - 6)(x - 6)
(x + 6)(x + 6)
(x + 3)(x + 12)
(x - 3)(x - 12)
(x - 6)(x - 6)
(x + 6)(x + 6)
(x + 3)(x + 12)
(x - 3)(x - 12)