\(f\left(x;y\right)=\frac{1}{2}\left(4x^4-4x^2+1\right)+\left(y^2-2y+1\right)-\frac{3}{2}\)
\(=\frac{1}{2}\left(2x^2-1\right)^2+\left(y-1\right)^2-\frac{3}{2}\ge-\frac{3}{2}\)
Dấu "=" xảy ra khi \(\left\{{}\begin{matrix}x^2=\frac{1}{2}\\y=1\end{matrix}\right.\)