\(A=-x^2+6x-11=-\left(x^2-6x+9\right)-2=-\left(x-3\right)^2-2\)
Vì: \(-\left(x-3\right)^2\le0\Rightarrow-\left(x-3\right)^2-2\le-2\)
Dấu ''='' xảy ra khi x = 3
Vậy MaxA = -2 <=> x = 3
\(A=-x^2+6x-11\\ =-x^2+6x-9-2\\ =-\left(x^2-6x+9\right)-2\\ =-\left(x-3\right)^2-2\le-2\forall x\)
Dấu "=" xảy ra khi:
\(x-3=0\\ \Leftrightarrow x=3\)
Vậy.................