So I was working on a study guide and got to a problem I cannot figure out. I won't have time to ask my professor about it before the test so I am just gonna post here.

$\displaystyle f(x)=4x^2-4x+21$

The vertex should be: 1/2 , 20

I understand the 1/2 part, but I can't get 20 no matter what I do. I am almost positive I am just leaving something out.