The steps in writing f(x) = 18x + 3x2 in vertex form are shown, but a value is missing in the last step. write the function in standard form. f(x) = 3x2 + 18x factor a out of the first two terms. f(x) = 3(x2 + 6x) form a perfect square trinomial. f(x) = 3(x2 + 6x + 9) – 3(9) write the trinomial as a binomial squared. f(x) = 3(x + – 27 what is the missing value in the last step?