2. Find and classify the local maximum, local minimum, and saddle points of the function $f(x,y) = x^2 + 4xy + y^4$.
3. Find the absolute maximum and minimum values of $f(x, y) = x^2 + y^2 + x^2y + 4$ on the square with vertices $(1, 1), (1, -1), (-1, -1)$ and $(-1, 1)$.