What does the matrix represent and why can't we use a 2x2 matrix? What does each part of the matrix represent?

4. Suppose that the following functions are used in optimization: (a) Z = XY (X, Y20) (b) Z = Y - InX (X, YZO) Assuming that the first-order conditions for maximum or minimum hold in both cases, determine whether there is a maximum or minimum in each case. Answer (a) Z = XY ( X, Y20) Zx = Y, Zy = X Zxx = 0, ZYY = 0, ZxY = 1, Zyx = 1 0 1 Y 1 O X = D = 2XY Y X ( 0 Y D1 = = -Y'S0 YO