1. Consider the function defined for all real r and y by f(x, y) = re^(-y) - 4y.
a) Find all the critical points of f. Then classify them by using the second-order conditions.
b) Show that f has neither a global maximum nor a global minimum.
c) Let S = {(x, y): 0 ≤ x ≤ 5, 0 ≤ y ≤ 4}. Prove that f has global maximum and minimum points in S, then find them.
d) Find the slope of the tangent to the level curve xe^(-y) - 4y = e^(-4) at the point where x = 1 and y = 4 - e.