f(x) = x2 + 4x - 12 Which of the following is the vertex form of f(x) ?
a. f(x) = (x + 4)2 - 12
b. f(x) = (x + 2)2 - 12
c. f(x) = (x + 4)2 - 28
d. f(x) = (x + 2)2 - 16