\(B=-x^2+4x+4=-\left(x^2-4x+4\right)+4+4=-\left(x-2\right)^2+8\)
Vì \(-\left(x-2\right)^2\le0\Rightarrow-\left(x-2\right)^2+8\le8\Leftrightarrow B\le8\)
Dấu ''='' xảy ra \(\Leftrightarrow-\left(x-2\right)^2=0\Rightarrow x-2=0\Rightarrow x=2\)
Vậy maxB=8 khi x=2