这题和上面讨论有相关 ※ 引述《taiyaki35 (小侠)》之铭言： : 来源: 黄贞颖老师考古题 : 科目: 个经 : 问题: : Consumer's surplus: A consumer has the utility function : U(x,y) =e^((ln(X)+Y)^1/3) : where X is the good in concern and Y is the money : that can be spent on all other goods. (So the price of Y is normalized to : be 1). The income of this consumer is 100. : (a) (10pts) Derive the demand function of x for this consumer. Make sure that : at every price of x, the consumer always has enough income to buy the amount : of x as indicated by hiss demand function. : (b) (10pts) Calculate the price elasticity of the demand function in (a). : Is it true that the absolute value of the elasticity of the demand decreases : as the amount of x increases? : (c) (10pts) Suppose price of x decreases from 2 to 1. Calculate the change : in consumer's surplus. : (d) (10pts) Suppose price of x decreases from 2 to 1. Calculate the : compensating variation of this price change. : (e) (10pts) Suppose price of x decreases from 2 to 1. Calculate the : equivalent variation of this price change . 令G(x,y)=(ln(X)+Y) 则U=V(G)=e^(G^1/3), 只要同样的G就会产生同样的U dU = V'(G) dG = V'(G) (1/x dX + dY) 又C=PX + Y => dC = P dX + DY 相切时有 V'(G)/x /P = V'(G)/1 消掉V'(G) 1/x / P = 1/1 =t 此例直接解出t=1 则切点 x=1/P (a)任意价格P任意预算下最佳消费 X=1/P (b) d(lnX)/d(lnP) = -1 则 elasticity=1 (c) X dP = 1/P dP = d(lnP), consumer's surplus: ln2-ln1 = ln2 (d) 先限C求U(求G即可): X=1/P , Y= C-PX = C-1=99 代入 G = ln(1/P) + Y = 99-lnP P由2 to 1 则 Gs 由 99-ln2 变 Ge = 99 然後再限G求C: X=1/P Y=G-lnX= G+lnP 代入 C=PX+Y=1+G+lnP compensating variation: 用原等效用线G=Gs, C=1+Gs+lnP=1+99-ln2+lnP delta C =delta lnP => 答案为 ln2 (e)equivalent variation用新等效用线G=Ge=99, C=1+99+lnP delta C =delta lnP => 答案为 ln2 --

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