Bài 1:
\(A=4x^2-4x+2019\)
\(=4x^2-4x+1+2018\)
\(=\left(2x-1\right)^2+2018\ge2018\)
\(Amin=2018\Leftrightarrow2x-1=0\)
\(\Leftrightarrow2x=1\)
\(\Leftrightarrow x=\frac{1}{2}\)
Bài 2:
\(B=-x^2+5x-2020\)
\(=-\left(x^2-5x+2020\right)\)
\(=-\left(x^2-5x+\frac{25}{4}-\frac{25}{4}+2020\right)\)
\(=-\left(x-\frac{5}{2}\right)^2-\frac{8055}{4}\le\frac{-8055}{4}\)
\(Bmax=\frac{-8055}{4}\Leftrightarrow x-\frac{5}{2}=0\)
\(\Leftrightarrow x=\frac{5}{2}\)
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