【正文】 s ?Q: When is a consumption bundle (x1, … , x n) affordable at given prices p1, … , p n? 76 Budget Constraints ?A: When p1x1 + … + p nxn ? m where m is the consumer‘s (disposable) ine. 77 Budget Constraints ?The bundles that are only just affordable form the consumer‘s budget constraint. This is the set { (x1,…,x n) | x1 ? 0, …, x n ??? and p1x1 + … + p nxn = m }. 78 Budget Constraints ?The consumer‘s budget set (預(yù)算集）is the set of all affordable bundles。1 教材 Intermediate Microeconomics: A Modern Approach (Sixth Edition) by Hal R. Varian W. W. Norton， 2022 2 ?參考書(shū)目： 《 微觀經(jīng)濟(jì)學(xué) 》 ，周惠中，上海人民出版社 ? 《 微觀經(jīng)濟(jì)學(xué) 》 ，范家驤，劉文忻，東北財(cái)經(jīng)大學(xué)出版社 ?參考習(xí)題冊(cè)： 《 微觀經(jīng)濟(jì)學(xué)：現(xiàn)代觀點(diǎn) 》 練習(xí)冊(cè)，伯格斯特龍、范里安著，費(fèi)方域等譯，上海三聯(lián)書(shū)店，上海人民出版社。 B(p1, … , p n, m) = { (x1, … , x n) | x1 ? 0, … , x n ??0 and p1x1 + … + p nxn ? m } ?The budget constraint is the upper boundary of the budget set. 79 Budget Set and Constraint for Two Commodities x2 x1 Budget constraint is p1x1 + p2x2 = m. m /p1 m /p2 80 Budget Set and Constraint for Two Commodities x2 x1 Budget constraint is p1x1 + p2x2 = m. m /p2 m /p1 81 Budget Set and Constraint for Two Commodities x2 x1 Budget constraint is p1x1 + p2x2 = m. m /p1 Just affordable m /p2 82 Budget Set and Constraint for Two Commodities x2 x1 Budget constraint is p1x1 + p2x2 = m. m /p1 Just affordable Not affordable m /p2 83 Budget Set and Constraint for Two Commodities x2 x1 Budget constraint is p1x1 + p2x2 = m. m /p1 Affordable Just affordable Not affordable m /p2 84 Budget Set and Constraint for Two Commodities x2 x1 p1x1 + p2x2 = m is x2 = (p1/p2)x1 + m/p2 so slope is p1/p2. m /p1 Budget Set m /p2 85 Budget Constraints x2 x1 +1 p1/p2 Opp. cost of an extra unit of modity 1 is p1/p2 units foregone of modity 2. 86 Budget Constraints x2 x1 Opp. cost of an extra unit of modity 1 is p1/p2 units foregone of modity 2. And the opp. cost of an extra unit of modity 2 is p2/p1 units foregone of modity 1. p2/p1 +1 87 預(yù)算集特點(diǎn) –在價(jià)格、收入給定的條件下，要增加 1單位 x1的消費(fèi)就必須減少 p1/p2的消費(fèi)。 . x y and y z x z. ~ f ~ f ~ f 135 Indifference Curves ?Take a reference bundle x‘. The set of all bundles equally preferred to x‘ is the indifference curve containing x‘。 ?邊際支付意愿 166 Marginal Rate of Substitution x2 x1 MRS at x‘ is lim {Dx2/Dx1} Dx1 0 = dx2/dx1 at x‘ Dx2 Dx1 x‘ 167 MRS amp。 Ind. Curve Properties Good 2 Bad 1 One good and one bad a positively sloped indifference curve MRS 0. 169 邊際替代率遞減 Good 2 Good 1 MRS = 5 MRS = MRS always increases with x1 (bees less negative) if and only if preferences are strictly convex. 170 Chapter Four Utility 效用 171 outline ? Utility function (效用函數(shù)） – Definition – Monotonic transformation （ 單調(diào)轉(zhuǎn)換） – Examples of utility functions and their indifference curves ? Marginal utility （ 邊際效用） ? Marginal rate of substitution 邊際替代率 – MRS after monotonic transformation 172 Utility Functions ?A utility function U(x) represents a preference relation if and only if: x‘ x‖ U(x‘) U(x‖) x‘ x‖ U(x‘) U(x‖) x‘ ~ x‖ U(x‘) = U(x‖). ~ f p p 173 Utility Functions ?Utility is an ordinal (. ordering) concept. [序數(shù)效用 ] ?. if U(x) = 6 and U(y) = 2 then bundle x is strictly preferred to bundle y. But x is not preferred three times as much as is y. 174 效用函數(shù)與無(wú)差異曲線 ?Equal preference ? same utility level. ?Therefore, all bundles in an indifference curve have the same utility level. 175 Utility Functions amp。 Perfect Substitutes ?regards units of modities 1 and 2 as equivalent, ? then the modities are perfect substitutes ?only the total amount of the two modities in bundles determines their preference rankorder. 148 Extreme Cases of Indifference Curves。 88 ?影響預(yù)算集的因素： Ine and Price 89 Higher ine gives more choice Original budget set New affordable consumption choices x2 x1 Original and new budget constraints are parallel (same slope). 90 How do the budget set and budget constraint change as ine m decreases? Original budget set x2 x1 91 How do the budget set and budget constraint change as ine m decreases? x2 x1 New, smaller budget set Consumption bundles that are no longer affordable. Old and new constraints are parallel. 92 Budget Constraints Price Changes ?What happens if just one price decreases? ?Suppose p1 decreases. 93 How do the budget set and budget constraint change as p1 decreases from p1’ to p1”? Original budget set x2 x1 m/p2 m/p1‘ m/p1‖ p1‘/p2 94 How do the budget set and budget constraint change as p1 decreases from p1’ to p1”? Original budget set x2 x1 m/p2 m/p1‘ m/p1‖ New affordable choices p1‘/p2 95 How do the budget set and budget constraint change as p1 decreases from p1’ to p1”? Original budget set x2 x1 m/p2 m/p1‘ m/p1‖ New affordable choices Budget constraint pivots。 3 The Theory of Economics does not furnish a body of settled conclusions immediately applicable to policy. It is a method rather than a doctrine, an apparatus of the mind, a technique of thinking which helps its possessor to draw correct conclusions John Maynard Keynes 4 Is Economics Useful? ?Being a thinker ?Changes the way you view life and understand problems ?An all