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1、DemandRelationshipsCHAPTERSIXamongGoodsInChapter5weexaminedhowchangesinthepriceofaparticulargood(say,goodx)affectthequantityofthatgoodchosen.Throughoutthediscussion,weheldthepricesofallothergoodsconstant.Itshouldbeclear,however,thatachangeinoneoftheseo
2、therpricescouldalsoaffectthequantityofxchosen.Forexample,ifxweretakentorepresentthequantityofautomobilemilesthatanindividualdrives,thisquantitymightbeexpectedtodecreasewhenthepriceofgasolineincreasesorincreasewhenairandbusfaresincrease.Inthischapterwew
3、illusetheutility-maximizationmodeltostudysuchrelationships.TheTwo-GoodCaseWebeginourstudyofthedemandrelationshipamonggoodswiththetwo-goodcase.Unfortunately,thiscaseprovestoberatheruninterestingbecausethetypesofrelation-shipsthatcanoccurwhenthereareonly
4、twogoodsarelimited.Still,thetwo-goodcaseisusefulbecauseitcanbeillustratedwithtwo-dimensionalgraphs.Figure6.1startsourex-aminationbyshowingtwoexamplesofhowthequantityofxchosenmightbeaffectedbyachangeinthepriceofy.Inbothpanelsofthefigure,pyhasdecreased.Th
5、ishastheresultofshiftingthebudgetconstraintoutwardfromI0toI1.Inbothcases,thequantityofgoodychosenhasalsoincreasedfromy0toy1asaresultofthedecreaseinpy,aswouldbeexpectedifyisanormalgood.Forgoodx,however,theresultsshowninthetwopanelsdiffer.In(a),theindiff
6、erencecurvesarenearlyL-shaped,implyingafairlysmallsubstitutioneffect.AdecreaseinpydoesnotinducealargemovealongU0asyissubstitutedforx.Thatis,xdropsrelativelylittleasaresultofthesubstitution.Theincomeeffect,however,reflectsthegreaterpurchasingpowernowavai
7、lable,andthiscausesthetotalquantityofxchosentoincrease.Hence@x/@pyisnegative(xandpymoveinoppositedirections).InFigure6.1bthissituationisreversed:@x/@pyispositive.Therelativelyflatindiffer-encecurvesinFigure6.1aresultinalargesubstitutioneffectfromthefall
8、inpy.ThequantityofxdecreasessharplyasyissubstitutedforxalongU0.AsinFigure6.1a,theincreasedpurchasingpowerfromthedecreaseinpycausesmorextobebought,butnowthesubstitutioneffectdominatesandthequantityofxdecreasestox1.Inthiscase,xandpythenmo
