Nech�
$$
f(x,y) = \cases \frac{x^3y  + x^2y + y^3}{x^2 + y^2} & (x,y) \not
                                                        = (0,0),\\
                0 & (x,y) = (0,0).
          \endcases
$$
\roster
\item"a)" Je $f$ spojit� v $(0,0)?$
\item"b)" M� $f$ tot�ln� diferenci�l v $(0,0)?$
\endroster
