生产成本教学文案

Chapter13TheCostsofProductionTheMarketForcesofSupplyandDemandSupplyanddemandarethetwowordsthateconomistsusemostoften.Supplyanddemandaretheforcesthatmakemarketeconomieswork.Modernmicroeconomicsisaboutsupply,demand,andmarketequilibrium.13.1WhatAreCosts?AccordingtotheLawofSupply:Firmsarewillingtoproduceandsellagreaterquantityofagoodwhenthepriceofthegoodishigh.Thisresultsinasupplycurvethatslopesupward.TheFirm’sObjective:Theeconomicgoalofthefirmistomaximizeprofits.MaximumProfits13.1.1TotalRevenue,TotalCost,andProfitTotalRevenue

Theamountafirmreceivesforthesaleofitsoutput.

TotalCost

Themarketvalueoftheinputsafirmusesinproduction.

Profit

isthefirm’stotalrevenueminusitscost.Profit=Totalrevenue–Totalcost13.1.2CostsasOpportunityCostsThisdistinctionbetweenexplicitandimplicitcostshighlightsanimportantdifferencebetweenhoweconomistsandaccountantsanalyzeabusiness.Economistsareinterestedinstudyinghowfirmsmakeproductionandpricingdecisions.Becausethesedecisionsarebasedonbothexplicitandimplicitcosts,economistsincludebothwhenmeasuringafirm’scost.Bycontrast,accountantshavethejobofkeepingtrackofthemoneythatflowsintoandoutoffirms.Asaresult,theymeasuretheexplicitcostsbutoftenignoretheimplicitcost.13.1.4EconomicProfitversusAccountingProfitEconomistsmeasureafirm’seconomicprofitastotalrevenueminustotalcost,includingbothexplicitandimplicitcosts.Accountantsmeasureafirm’saccountingprofitasthefirm’stotalrevenueminusonlythefirm’sexplicitcosts.Whentotalrevenueexceedsbothexplicitandimplicitcosts,thefirmearnseconomicprofit.Economistsprofitissmallerthanaccountingprofit.Figure1EconomicversusAccountantsCopyright©2004South-WesternRevenueTotalopportunitycostsHowanEconomistViewsaFirmHowanAccountantViewsaFirmRevenueEconomicprofitImplicitcostsExplicitcostsExplicitcostsAccountingprofitEconomistsincludeallopportunitycostswhenanalyzingafirm,whereasaccountantmeasureonlyexplicitcosts.Therefore,economicprofitissmallerthanaccountingprofit.HowanEconomistViewsaFirmRevenueTotalopportunitycostsEconomicprofitHowanAccountantsViewsaFirmRevenueAccountingprofitImplicitcostsExplicitcostsExplicitcostsFigure1EconomistsversusAccountantsTable1AProductionFunctionandTotalCost:HungryHelen’sCookiesFactoryNumberofWorkersOutput(quantityofcookiesproducedperhour)MarginalProductofLaborCostofFactoryTotalCostofInputs(costoffactory+costofworkers)CostofWorkers00$30$0$30150301040290302050312030306041403040705150305080504030201013.2ProductionandCostsTheProductionFunctionTheProductionfunctionshowstherelationshipbetweenquantityofinputsusedtomakeagoodandthequantityofoutputofthatgood.MarginalProductTheMarginalproductofanyinputintheproductionprocessistheincreaseinoutputthatarisesfromanadditionalunitofthatinput.13.2TheProductionFunctionDiminishingMarginalProduct

Diminishingmarginalproductisthepropertywherebythemarginalproductofaninputdeclinesasthequantityoftheinputincreases.Example:Asmoreandmoreworkersarehiredatafirm,eachadditionalworkercontributeslessandlesstoproductionbecausethefirmhasalimitedamountofequipment.Aproductionfunctionshowstherelationshipbetweenthenumberofworkershiredandthequantityofoutputproduced.Herethenumberofworkershired(onthehorizontalaxis)isfromthefirstcolumninTable13-1,andthequantityofoutputproduced(ontheverticalaxis)isfromthesecondcolumn.Theproductionfunctiongetsflatterasthenumberofworkersincrease,whichreflectsdiminishingmarginalproduct.QuantityofOutput(cookiesperhour)NumberofWorkersHiredProductionfunction10234540206080100120140Figure2HungryHelen’sProductionFunction13.2.1TheProductionFunctionDiminishingMarginalProductTheslopeoftheproductionfunctionmeasuresthemarginalproductofaninput,suchasaworker.Whenthemarginalproductdeclines,theproductionfunctionbecomesflatter.13.2.2FromtheProductionFunctiontotheTotal-CostCurveTherelationshipbetweenthequantityafirmcanproduceanditscostsdeterminespricingdecisions.Thetotal-costcurveshowsthisrelationshipgraphically.Table1AProductionFunctionandTotalCost:HungryHelen’sCookiesFactoryNumberofWorkersOutput(quantityofcookiesproducedperhour)MarginalProductofLaborCostofFactoryTotalCostofInputs(costoffactory+costofworkers)CostofWorkers00$30$0$301503010402903020503120303060414030407051503050805040302010Atotal-costcurveshowstherelationshipbetweenthequantityofoutputproducedandtotalcostofproduction.Herethequantityofoutputproduced(onthehorizontalaxis)isfromthesecondcolumninTable13-1,andthetotalcost(ontheverticalaxis)isfromthesixthcolumn.Thetotal-costcurvegetssteeperasthequantityofoutputincreasesbecauseofdiminishingmarginalproduct.QuantityofOutput(cookiesperhour)TotalCostTotal-costcurve2004060801002010304060$807050120140Figure3HungryHelen’sTotal-CostCurveFromtheProductionFunctiontotheTotal-CostCurveNowcomparethetotal-costcurveinFigure3withtheproductionfunctioninFigure2.Thesetwocurvesareoppositesidesofthesamecoin.Thetotal-costcurvegetssteeperastheamountproducedrises,whereastheproductionfunctiongetsflatterasproductionrises.Thesechangesinslopeoccurforthesamereason.HighproductionofcookiesmeansthatHelen’skitcheniscrowdedwithmanyworkers.Becausethekitcheniscrowded,eachadditionalworkeraddslesstoproduction,reflectingdiminishingmarginalproduct.Therefore,theproductionfunctionisrelativelyflat.Butnowturnthislogicaround:Whenthekitcheniscrowded,producinganadditionalcookierequiresalotofadditionallaborandisthusverycostly.Therefore,whenthequantityproducedislarge,thetotal-costcurveisrelativelysteep.(Mankiw,thirdedition,p274)Costsofproductionmaybedividedintofixedcosts

and

variablecosts.Fixedcostsarethosecoststhatdonotvarywiththequantityofoutputproduced.Variablecostsarethosecoststhatdovarywiththequantityofoutputproduced.TotalcostsTotalFixedcosts(TFC)TotalVariablecosts(TVC)Totalcosts(TC)TC=TFC+TVC13.3.1FixedandVariableCostsTable2TheVariousMeasuresofCost:ThirstyThelma’sLemonadeStandQuantityofLemonade(glassesperhour)TotalCostVariableCostAverageFixedCostMarginalCost0$3.00$3.00$0.00---$0.300.50FixedCostAverageVariableCostAverageTotalCost13.303.000.30$3.00$0.30$3.3023.803.000.801.500.401.9034.503.001.501.000.501.50912.903.009.900.331.101.431015.003.0012.800.301.201.5079.303.006.300.430.901.3345.403.002.400.750.601.3556.503.003.500.600.701.3067.803.004.800.500.801.30811.003.008.000.381.001.380.700.901.101.301.501.701.902.10AveragecostsAveragecostscanbedeterminedbydividingthefirm’scostsbythequantityofoutputitproduces.Theaveragecostisthecostofeachtypicalunitofproduct.13.3.2AverageandMarginalCostsAveragecostsAverageFixedcosts(AFC)AverageVariablecosts(AVC)AverageTotalcosts(ATC)ATC=AFC+AVC13.3.2AverageandMarginalCostsAverageCosts

AFC==AVC==ATC==FixedcostQuantityFCQVariablecostQuantityVCQTotalcostQuantityTCQTable2TheVariousMeasuresofCost:ThirstyThelma’sLemonadeStandQuantityofLemonade(glassesperhour)TotalCostVariableCostAverageFixedCostMarginalCost0$3.00$3.00$0.00---$0.300.50FixedCostAverageVariableCostAverageTotalCost13.303.000.30$3.00$0.30$3.3023.803.000.801.500.401.9034.503.001.501.000.501.50912.903.009.900.331.101.431015.003.0012.800.301.201.5079.303.006.300.430.901.3345.403.002.400.750.601.3556.503.003.500.600.701.3067.803.004.800.500.801.30811.003.008.000.381.001.380.700.901.101.301.501.701.902.10Marginalcosts

Marginalcosts(MC)measurestheincreasesintotalcostthatarisesfromanextraunitofproduction.Marginalcosthelpsanswerthefollowingquestion:Howmuchdoesitcosttoproduceanadditionalunitofoutput?13.3.2AverageandMarginalCostsMarginalCosts

MC==

(changeintotalcost)△TC△Q(changeinquantity)

RelationshipsAmongCost&ProductionFunctionsAP&AVCareinverselyrelated.(ex:oneinput)AVC=(W

L)/Q=W/(Q/L)=W/APLAsAPLrises,AVCfallsMPandMCareinverselyrelated

MC=dTC/dQ=(W

dL)/dQ=W/(dQ/dL)=W/MPLAsMPLdeclines,MCrisesprod.functionscostfunctionsMPLLMCAP

AVC(Figure8.3onpage358)QQcostMarginalCost

ThirstyThelma’sLemonadeStandFigure4ThirstyThelma’sTotal-CostCurvesCopyright©2004South-WesternTotalCost$15.0014.0013.0012.0011.0010.009.008.007.006.005.004.003.002.001.00QuantityofOutput(glassesoflemonadeperhour)014327659810Total-costcurveHerethequantityofoutputproduced(onthehorizontalaxis)isfromthefirstcolumninTable13-2,andthetotalcost(ontheverticalaxis)isfromthesecondcolumn.AstheFigure13-3,thetotal-costcurvegetssteeperasthequantityofoutputincreasesbecauseofdiminishingmarginalproduct.TotalCostQuantityofOutput(glassesoflemonadeperhour)Total-CostCurve1023454.002.006.008.0010.0012.0014.00$15.00678910Figure4ThirtyThelma’sTotal-CostCurvesFigure5ThirstyThelma’sAverage-CostandMarginal-CostCurvesCopyright©2004South-WesternCosts$3.503.253.002.752.502.252.001.751.501.251.000.750.500.25QuantityofOutput(glassesoflemonadeperhour)014327659810MCATCAVCAFCCostsQuantityofOutput(glassesoflemonadeperhour)1023451.000.501.502.002.503.003.50678910MCAVCATCAFCFigure5ThirstyThelma’sAverage-CostandMarginal-CostCurvesFigure5ThirstyThelma’sAverage-CostandMarginal-CostCurveThisfigureshowstheaveragetotalcost(ATC),averagefixedcost(AFC),averagevariablecurve(AVC),andmarginalcost(MC)forThirstyThelma’sLemonadeStand.AllofthesecurvesareobtainedbygraphingthedatainTable13-2.Thesecostcurvesshowthreefeaturesthataretypicalofmanyfirms:(1)Marginalcostriseswiththequantityofoutput.(2)Theaverage-total-costcurveisU-shaped.(3)Themarginal-costcurvecrossestheaverage-total-costcurveattheminimumofaveragetotalcost.Marginalcostriseswiththeamountofoutputproduced.Thisreflectsthepropertyofdiminishingmarginalproduct.13.3.3CostCurvesandTheirShapesCostsQuantityofOutput(glassesoflemonadeperhour)1023451.000.501.502.002.503.003.50678910MCFigure5ThirstyThelma’sAverage-CostandMarginal-CostCurvesTheaveragetotal-costcurveisU-shaped.Atverylowlevelsofoutputaveragetotalcostishighbecausefixedcostisspreadoveronlyafewunits.Averagetotalcostdeclinesasoutputincrease.Averagetotalcoststartsrisingbecauseaveragevariablecostrisessubstantially.13.3.3CostCurvesandTheirShapesThebottomoftheU-shapedATCcurveoccursatthequantitythatminimizesaveragetotalcost.Thisquantityissometimescalledtheefficientscaleofthefirm.13.3.3CostCurvesandTheirShapesCostsQuantityofOutput(glassesoflemonadeperhour)1023451.000.501.502.002.503.003.50678910ATCFigure5ThirstyThelma’sAverage-CostandMarginal-CostCurvesRelationshipbetweenMarginalcostandAverageTotalCost.Whenevermarginalcostislessthanaveragetotalcost,averagetotalcostisfalling.Whenevermarginalcostisgreaterthanaveragetotalcost,averagetotalcostisrising.13.3.3CostCurvesandTheirShapesRelationshipbetweenMarginalcostandAverageTotalCost.Themarginal-costcurvecrossedtheaverage-total-costcurveattheefficientscale.Efficientscaleisthequantitythatminimizesaveragetotalcost.13.3.3CostCurvesandTheirShapesCostsQuantityofOutput(glassesoflemonadeperhour)1023451.000.501.502.002.503.003.50678910MCATCFigure5ThirstyThelma’sAverage-CostandMarginal-CostCurvesItisnowtimetoexaminetherelationshipsthatexistbetweenthedifferentmeasuresofcost.13.3.4TypicalCostCurvesQuantityofLemonade(glassesperhour)TotalCostVariableCostAverageFixedCostMarginalCost0$2.00$2.00$0.00---$1.000.80FixedCostAverageVariableCostAverageTotalCost13.002.001.00$2.00$1.00$3.0023.802.001.801.000.901.9034.402.002.400.670.801.4798.802.006.800.220.760.981010.202.008.200.200.821.0276.602.004.600.290.660.9544.802.002.800.500.701.2055.202.003.200.400.641.0465.802.003.800.330.630.9687.602.005.600.250.700.950.600.400.400.600.801.001.201.401111.802.009.800.180.891.071213.602.0011.600.170.971.141315.602.0013.600.151.051.201417.802.0015.800.141.131.271.601.802.002.20BigBob’sCostCurvesFigure6BigBob’sCostCurvesCopyright©2004South-Western(a)Total-CostCurve$18.0016.0014.0012.0010.008.006.004.00QuantityofOutput(bagelsperhour)TC42681412102.00TotalCost0(a)Total-CostCurve$18.002.004.006.008.0010.0012.0014.0016.00TotalCost02461081214QuantityofOutput(bagelsperhour)TCFigure6BibBob’sCostCurvesFigure6BigBob’sCostCurves(b)Marginal-andAverage-CostCurvesQuantityofOutput(bagelsperhour)Costs$3.002.502.001.501.000.5004268141210MCATCAVCAFC(b)Marginal-andAverage-CostCurves0.501.001.50Costs2.002.50$3.0062481014120QuantityofOutput(bagelsperhour)AFCAVCATCMCFigure6BibBob’sCostCurvesFigure6.BigBob’sCostCurve.Manyfirms,likeBigBob’sBin,experienceincreasingmarginalproductbeforediminishingmarginalproductand,therefore,havecostcurvesshapedlikethoseinthisfigure.Panel(a)showshowtotalcost(TC)dependsonthequantityproduced.Panel(b)showshowaveragetotalcost(ATC),averagefixedcost(AFC),averagevariablecurve(AVC),andmarginalcost(MC)dependsonthequantityproduced.Thesecurvesarederivedbygraphingthedatafromthetable.Noticethatmarginalcostandaveragevariablecostfallforawhilebeforestartingtorise.13.3.4TypicalCostCurvesThreeImportantPropertiesofCostCurvesMarginalcosteventuallyriseswiththequantityofoutput.Theaverage-total-costcurveisU-shaped.Themarginal-costcurvecrossestheaverage-total-costcurveattheminimumofaveragetotalcost13.4CostsintheShortrunandintheLongRunFormanyfirms,thedivisionoftotalcostsbetweenfixedandvariablecostsdependsonthetimehorizonbeingconsidered.Intheshortrun,somecostsarefixed.Inthelongrun,fixedcostsbecomevariablecosts.Becausemanycostsarefixedintheshortrunbutvariableinthelongrun,afirm’slong-runcostcurvesdifferfromitsshort-runcostcurves.Figure7AverageTotalCostintheShortandLongRunCopyright©2004South-WesternQuantityofCarsperDay0AverageTotalCost1,200$12,000ATC

inshortrunwithsmallfactoryATC

inshortrunwithmediumfactoryATC

inshortrunwithlargefactoryATC

inlongrunSourcesofIncreasingReturnstoScaleThesourcesofincreasingoutputperunitofinputwhenafirmgrowsincludetechnical,managerial,purchasing,marketingandfinancialeconomies.EconomiesandDiseconomiesofScale

Economiesofscale(increasingreturnstoscale)refertothepropertywherebylong-runaveragetotalcostfallsasthequantityofoutputincreases.Diseconomiesofscale(decreasingreturnstoscale)refertothepropertywherebylong-runaveragetotalcostrisesasthequantityofoutputincreases.

Constantreturnstoscalereferstothepropertywherebylong-runaveragetotalcoststaysthesameasthequantityofoutputincreases.Figure7AverageTotalCostintheShortandLongRunCopyright©2004South-WesternQuantityofCarsperDay0AverageTotalCost1,200$12,0001,00010,000EconomiesofscaleATC

inshortrunwithsmallfactoryATC

inshortrunwithmediumfactoryATC

inshortrunwithlargefactoryATC

inlongrunDiseconomiesofscaleConstantreturnstoscaleBecausefixedcostsarevariableinthelongrun,theaverage-total-costintheshortrundiffersfromtheaverage-total-costcurveinthelongrun.QuantityofCarsperDayAverageTotalCostATCinshortrunwithsmallfactory01,000$12,00010,0001,200ATCinshortrunwithmediumfactoryATCinshortrunwithlargefactoryConstantreturnstoscaleEconomiesofscaleDiseconomiesofscaleATCinlongrunFigure7AverageTotalCostintheShortandLongRunsTheterms“economiccosts,”thatinclude“normalprofits,”and“economicprofits”thatarenotincludedin“economicscosts”areoftenconfusing.Usingtheterm“excessoreconomicprofits”helps.Economistsclassifynormalprofitsascosts,sinceinthelongruntheownerofafirmwouldcloseitdownifanormalprofitwerenotbeingearned.Sinceanormalprofitisrequiredtokeeptheentrepreneuroperatingthefirm,anormalprofitisacost.Economicprofitsarenotcostsofproductionsincetheentrepreneurdoesnotrequirethegainingofaneconomicprofittokeepthefirmoperating.Ineconomics,costsarewhateverisrequiredtokeepafirmoperating.(McConnell,Economics,15edition,ch22productioncost.)SummaryThegoaloffirmsistomaximizeprofit,whichequalstotalrevenueminustotalcost.Whenanalyzingafirm’sbehavior,itisimportanttoincludealltheopportunitycostsofproduction.Someopportunitycostsareexplicitwhileotheropportunitycostsareimplicit.SummaryAfirm’scostsreflectitsproductionprocess.Atypicalfirm’sproductiongetsflatterasthequantityofinputincreases,displayingthepropertyofdiminishingmarginalproduct.Afirm’stotalcostsaredividedbetweenfixedandvariablecosts.Fixedcostsdonochangewhenthefirmaltersthequantityofoutputproduct,variablecostsdochangeasthefirmaltersquantityofoutputproduced.SummaryAveragetotalcostistotalcostdividedbythequantityofoutput.Marginalcostistheamountbywhichtotalcostwouldriseifoutputwereincreasedbyoneunit.Themarginalcostalwaysriseswiththequantityofoutput.Averagecostfirstfallsasoutputincreasesandthenrises.SummaryTheaverage-total-costcurveisU-shaped.Themarginal-costcurvealwayscrossestheaverage-total-costcurveattheminimumofATC.Afirm’scostsoftendependonthetimehorizonbeingconsidered.Inparticular,manycostsarefixedintheshortrunbutvariableinthelongrun.Mankiw-chapter13.ProblemandAnswer5.假定某厂商的边际成本函数，且生产10单位产量时的总成本为1000。求:(1)固定成本的值。(2)总成本函数、总可变成本函数，以及平均成本函数、平均可变成本函数。(高鸿业《西方经济学》第三版，第五章成本论)Mankiw-chapter13.ProblemandAnswerProblemandAnswer6.某公司用两个工厂生产一种产品，其总成本函数为，其中Q1表示第一个工厂生产的产量，Q2表示第二个工厂生产的产量。求：当公司生产的产量为40时能够使得公司生产成本最小的两工厂的产量组合.(高鸿业《西方经济学》第三版，第五章成本论)ProblemandAnswer7.已知生产函数；各要素价格分别为PA＝1，PL＝1，PK＝2；假定厂商处于短期生产，且。推导：该厂商短期生产的总成本函数和平均成本函数；总可变成本函数和平均可变成本函数；边际成本函数。8.已知生产函数;当资本投入量K＝50时资本的总价格为500；劳动的价格PL＝5。求:(1)劳动的投入函数L=L(Q)(2)总成本函数、平均成本函数和边际成本函数。(3)当产品价格P＝100时，厂商获得最大利润的产量和利润各是多少？(高鸿业《西方经济学》第三版，第五章成本论)5、已知生产函数Q=min(L,4K)。求：（1）当产量Q=32时，L与K值分别是多少？（2）如果生产要素的价格分别为PL=2，PK=5，则生产100单位产量时的最小成本是多少？解答：（1）生产函数Q=min(L,4K)表示该函数是一个固定投入比例的生产函数，所以，厂商进行生产时，总有Q=L=4K。因为已知产量Q=32，所以，相应地有L=32，K=8。（2）由Q=L=4K，且Q=100，可得：L=100，K=25

又因PL=2，PK=5，所以有：

C=PL·L+PK·K=2×100+5×25=325

既生产100单位产量的最小成本为325。6、已知生产函数为

求：（1）厂商长期生产的扩展线方程。（2）当PL=1，PK=1，Q=1000时，厂商实现最小成本的要素投入组合。解答：（1）（a）关于生产函数由最优要素组合的均衡条件

（2）关于生产函数由最优要素组合的均衡条件

（c）关于生产函数（d）关于生产函数Q=min(3L,K)。

由于该函数是固定投入比例的生产函数，既厂商的生产总有3L=K，所以，直接可以得到厂商长期生产的扩展方程为K=3L。（2）关于生产函数（b）关于生产函数。

（c）关于生产函数

（d）关于生产函数7、已知生产函数为判断：（1）在长期生产中,该生产函数的规模报酬属于哪一种?（2）在短期生产中,该生产函数是否受边际报酬递减的支配?解答：（1）所以，生产函数属于规模报酬不变的生产函数。10.试用图从短期总成本曲线推导出长期总成本曲线，并说明长期总成本曲线的经济含义。11.试用图从短期平均成本曲线推导长期平均成本曲线，并说明长期平均成本曲线的经济含义。12.试用图从短期边际成本曲线推导长期边际成本曲线，并说明长期边际成本曲线的经济含义。(高鸿业《西方经济学》第三版，第五章成本论)ProblemandAnswerExerciseandAnswer3、为了实现既定成本条件下的最大产量或即定产量条件下的最小成本,如果企业处于

MRTSLK>

或者MRTSLK＜时,企业应该分别如何调整劳动和资本的投入量,以达到最优的要素组合?为什么?解答：要点如下：(1)研究给定条件下的产量最大化或成本最小化的分析工具是等产量曲线和等成本线。等产量曲线的斜率的绝对值可以用两要素的边际技术替代率MRTSLK

来表示,等成本线的斜率为-，即两要素的相对价格。在几何图形的分析中，生产者追求既定约束条件下的产量最大化或成本最小化的均衡点都发生在等产量曲线和等成本线的相切点上,于是有生产者最优生产要素组合的均衡条件为：MRTSLK=

。其经济含义为：在厂商的生产要素最优组合的均衡点上，厂商在生产中的两要素的边际技术替代比率(即MRTSLK)，即用一单位的劳动所替代的资本的数量，应该恰好等于该厂商能够在市场用一单位的劳动去交换资本的数量(即)。(2)在MRTSLK>时，厂商对生产要素投入组合的调整,可以用图1-19来说明。先看表示给定成本条件下的产量最大化的(a)图。在(a)图中的α点上有等产量曲线的斜率的绝对值大于等成本线斜率的绝对值，即MRTSLK>，且α点的要素投入组合为(L1,K1),相应的产量由等产量曲线Q1表示。但在成本给定(即等成本线AB给定)的条件下,a点的要素投入组合生产的产量并不是最大的。厂商应该从α点出发,沿着给定的表示约束条件的等成本线AB向均衡点E靠拢，比如说，由α点运动到α'点，则厂商就可以在不改变成本的条件下，将要素调整到(L2，K2)，从而达到更大的产量水平，此产量水平用过

α'点的等产量曲线Q2(虚线)来表示。很清楚，