1. [5 marks] Find the critical points of f(x,y) = xy(x - 2)(y + 3).
2. [6 mark] Find and classify all the critical points of f(x,y) = x^4 + 2y^2 + 4xy.
3. [6 marks] Find the maximum and minimum values of f(x,y) = y^2 + 6x^2 on the set R = {(x,y) | 2x^2 + y^2 ≤ 9}.