Zjist�te $\sup_{z \in M}f(z),$ $\inf_{z \in M}f(z)$ a
vy�et�ete, zda $f$ t�to hodnoty nab�v�.
$$
f(x,y) = x^2 + y^2 -2xy, \qquad M = \{(x,y) \in \Bbb R^2;\, x^2 +
\frac 14 y^2 \leq 1\}.
