A=-\(\left(x-\dfrac{1}{3}\right)^2-25\)
do \(\left(x-\dfrac{1}{3}\right)^2\ge0\forall x\)
=>-\(\left(x-\dfrac{1}{3}\right)^2\le0\)
=>-\(\left(x-\dfrac{1}{3}\right)^2-25\le-25\)
=> A\(\le\) -25
A Max = -25 khi
x-\(\dfrac{1}{3}=0\)
=> x=\(\dfrac{1}{3}\)
vậy A Mã =-25 khi x=\(\dfrac{1}{3}\)