Find the critical points of the function. Then use the Second Derivative Test to classify each critical point (or state that the test fails).
f(x, y) = x3 + y4 - 21x - 18y2
The Attempt at a Solution
partial x derivative=3x^2-21=0
partial y= 4y^3-36y=0
i try to solve those for numbers, but the answer space in the question has space for 6 different critical point answers, so I am not sure where to go from here.