The first three steps in writing f(x) = 40x + 5x2 in vertex form are shown.

write the function in standard form. f(x) = 5x2 + 40x
factor a out of the first two terms. f(x) = 5(x2 + 8x)
form a perfect square trinomial. = 16
f(x) = 5(x2 + 8x + 16) – 5(16)
what is the function written in vertex form?

a. f(x) = 5(x + 4) – 80
b. f(x) = 5(x + 8) – 80
c. f(x) = 5(x + 4)2 – 80
d. f(x) = 5(x + 8)2 – 80