1.下列效用函數,何者與U(x, y) = (x1/3 + 2y1/3)^3有相同的偏好?
(A)U(x, y) = 10 + 5(x1/3 + 2y1/3)
(B)U(x, y) = 2x1/3 y1/3
(C)U(x, y) = x1/3 + y1/3
(D)U(x, y) = ln 2 + ln x + ln y
答案:A
sol:
(A)
令U = (x^1/3 + 2y^1/3)^3
而V = 10 + 5(x^1/3 + 2y^1/3) = 10 + 5(U)^1/3
dV/dU = 5/3U^-2/3 > 0
因為結果不是實數,想請問該怎麼判斷是否大於0或小於0呢?