a, Ta có: \(\left(x-1\right)^4\ge0\forall x\)
Dấu "=" xảy ra \(\Leftrightarrow x=1\)
\(\Rightarrow M=\left(x-1\right)^4+\dfrac{1}{4}\ge\dfrac{1}{4}\forall x\)
Dấu "=" xảy ra \(\Leftrightarrow x=1\)
Vậy \(M_{min}=\dfrac{1}{4}\Leftrightarrow x=1\)
b, Ta có: \(\left(2x-1\right)^2\ge0\forall x\)
Dấu "=" xảy ra \(\Leftrightarrow x=\dfrac{1}{2}\)
\(\left|y-1\right|\ge0\forall y\)
Dấu "=" xảy ra \(\Leftrightarrow y=1\)
\(\Rightarrow N=3+\left(2x-1\right)^2+\left|y-1\right|\ge3\forall x,y\)
Dấu "=" xảy ra \(\Leftrightarrow\left\{{}\begin{matrix}x=\dfrac{1}{2}\\y=1\end{matrix}\right.\)
Vậy \(N_{min}=3\Leftrightarrow\left\{{}\begin{matrix}x=\dfrac{1}{2}\\y=1\end{matrix}\right.\)
