\(A=5-3\left(2x-1\right)^2\le5\)
Dấu "=" xảy ra khi: \(x=\dfrac{1}{2}\)
\(B=\dfrac{1}{2\left(x-1\right)^2+3}\le\dfrac{1}{3}\)
Dấu "=" xảy ra khi: \(x=1\)
\(C=x^4+3x^2+2\ge2\)
Dấu "=" xảy ra khi : \(\left\{{}\begin{matrix}x^4=0\\3x^2=0\end{matrix}\right.\Leftrightarrow x=0\)