Complete the square to write c (x) = x2 - 16x 84 in vertex form.

Group

c (x) = (x²-16x) + 84

take 1/2 of - 16 and square it

-16/2=-8, (-8) ²=64

ad negative and positive inside

c (x) = (x²-16x+64-64) + 84

factor

c (x) = ((x-8) ²-64) + 84

distribute or get rid of paenthsees

c (x) = (x-8) ²-64+84

add

c (x) = (x-8) ²+20