Ta có:\(B=-\left(x^2-2.\dfrac{1}{2}x+\dfrac{1}{4}\right)+\dfrac{1}{4}=-\left(x-\dfrac{1}{2}\right)^2+\dfrac{1}{4}\le\dfrac{1}{4}\)
Dấu "=: xảy ra \(\Leftrightarrow x=\dfrac{1}{2}\)
-( x^2 - 2x1/2 + 1/4) + 1/4
-(x - 1/2)^2 + 1/4 <=1/4
MaxB= 1/4 khi x=1/2
B=x-x2
= \(-x^2+2\dfrac{1}{2}x-\dfrac{1}{4}+\dfrac{1}{4}\)
=\(-\left(x^2-2\dfrac{1}{2}x+\dfrac{1}{4}\right)+\dfrac{1}{4}\)
=\(-\left(x-\dfrac{1}{2}\right)^2+\dfrac{1}{4}\)
Ta có ;
\(-\left(x-\dfrac{1}{2}\right)^2\le0\Rightarrow-\left(x-\dfrac{1}{2}\right)^2+\dfrac{1}{4}\le\dfrac{1}{4}\)
