Equations that could define f a. f (x) = (x 9) (x 3) 6. f (x) =-x? - 12x -18 c. f (x) = (x 6)3 9 d. f (x) = x? 12x 18 e. f (x) = (x 6)-9 f. f (x) = (x - 9) (x-3)