Problem 1 (25 points)
A. Find the total differential of U = (x1 - x2) / (2x1^2) (present the computational steps in a neat and structured manner) (4 points).
B. Find the extremum values of y = f(x1, x2) = x1^3/3 + x1x2 + x2^2 (present the computational steps in a neat and structured manner) (8 points).
C. Find the critical values of the function: y = x + 1/x (with x ≠ 0) and compare the "minimum" value with the "maximum" value (present the computational steps in a neat and structured manner) (5 points). How can you explain your result (3 points)?
D. Consider the following function: F(w, x, y) = x^2 + 3xy + 2yw + y^2 + w^2 - 11 = 0. Show that an implicit function w = g(x, y) is defined around point P (x = 1, y = 2, w = 0) (present your answer in a neat and structured manner) (3 points). Find ∂w/∂x and evaluate it at point P (2 points).