Let f (x, y) = x ^ 2 + y ^ 2 +4 kxy, k is a constant.
a) Show that f has a stationary point in (0.0) independent of the value of k.
b) For values of k, will have a saddle point (0.0)?
c) For values of k, will have a local minimum in (0.0)?
d) For k values is the criterion of second partial derivatives inclusive?