Classify the stationary points by looking directly at the

Question

(a) Find the domain of the function f (x, y) = ln(1 + x²y).

(b) Prove that the stationary points are all the points on the y-axis.

(c) Show that the second-derivative test fails.

(d) Classify the stationary points by looking directly at the sign of the value of f (x, y). Then look at the figure in the answer section.