Locate and classify all the local extrema of f(x, y) = 3x³ + 3y³ + 9xy − 3.
1. local max at (1, 1), saddle at (0, 0)
2. saddle at (−1, −1), local max at (0, 0)
3. local min at (−1, −1), saddle at (0, 0)
4. local min at (0, 0), local max at (−1, −1)
5. local max at (−1, −1), saddle at (0, 0)