Problem 3 Find all stationary points of the following R2 functions and classify them (only local): (a) f(x, y) = 1- y² — x¹. (b) f(x, y) = x² + y²

− 2x² + 4xy – 2y² (c) f(x, y) = (ax² + by²)e-²+y², where a, b € R.