Bài 1:
Ta thấy:\(2x^2\ge0\Rightarrow-2x^2\le0\)
\(\Rightarrow-2x^2-1\le-1\Rightarrow C\le-1\)
Dấu "=" khi \(-2x^2=0\Leftrightarrow x=0\)
Vậy \(Max_C=-1\) khi x=0
Ta thấy: \(3\sqrt{x-5}\ge0\)
\(\Rightarrow-3\sqrt{x-5}\le0\)
\(\Rightarrow-3\sqrt{x-5}+2\le2\)
\(\Rightarrow D\le2\)
Dấu "=" khi \(-3\sqrt{x-5}=0\Leftrightarrow\sqrt{x-5}=0\Leftrightarrow x-5=0\Leftrightarrow x=5\)
Vậy \(Max_D=2\) khi \(x=5\)
Bài 2:
Ta thấy: \(3x^2\ge0\Rightarrow3x^2-5\ge-5\)
\(\Rightarrow A\ge-5\)
Dấu "=" khi \(3x^2=0\Leftrightarrow x=0\)
Vậy \(Min_A=-5\) khi x=0
Ta thấy: \(2\left(x-3\right)^2\ge0\)
\(\Rightarrow B\ge0\)
Dấu "=" khi \(2\left(x-3\right)^2=0\Leftrightarrow\left(x-3\right)^2=0\Leftrightarrow x-3=0\Leftrightarrow x=3\)
Vậy \(Min_B=0\) khi x=3
