竞争的含义 The Meaning of Competition 竞争市场上的企业 ◆完全竞争市场具有下列特征 Firms in Competitive a perfectly competitive market has the Markets following characteristics: ●市场中有许多买者和卖者 第14章 There are many buvers and sellers in the Chapter 14 ◆名个卖者提供的物品大体上是相同的 oods offered by the various sellers are ◆企业可以自由地进入或退出市场 Firms can freely enter or exit the market 竞争的含义 The Meaning of Competition 竞争的含义 ◆这些特征,使得完全竞争市场具有如下结果: The Meaning of Competition As a result of its characteristics, the perfectly competitive market has the following outcomes: 竞争市场中的买者和卖者被称为价格 钡忽深政卖者的行动对市场价格的影确部 接受者。 The actions of any single buyer or seller in the Buyers and sellers in competitive narket have a negligible impact on the market markets are said to be price takers. ◆每一个买者和卖者都接受市场决定的价格 es the market price as 竞争企业的收益 竞争企业的收益 Revenue of a Competitive Firm Revenue of a Competitive Firm 企业的总收益是销售价乘以销售量。 Total revenue for a firm is the selling 总收益与产量成比例 price times the quantity sold. Total revenue is proportional to the amount of output TR=(PX QI
1 竞争市场上的企业 Firms in Competitive Markets 第14章 Chapter 14 2 竞争的含义 The Meaning of Competition 完全竞争市场具有下列特征: A perfectly competitive market has the following characteristics: 市场中有许多买者和卖者 There are many buyers and sellers in the market. 各个卖者提供的物品大体上是相同的 The goods offered by the various sellers are largely the same. 企业可以自由地进入或退出市场 Firms can freely enter or exit the market. 3 竞争的含义 The Meaning of Competition 这些特征，使得完全竞争市场具有如下结果： As a result of its characteristics, the perfectly competitive market has the following outcomes: 任何一个买者或卖者的行动对市场价格的影响都 可以忽略不计。 The actions of any single buyer or seller in the market have a negligible impact on the market price. 每一个买者和卖者都接受市场决定的价格。 Each buyer and seller takes the market price as given. 4 竞争的含义 The Meaning of Competition 竞争市场中的买者和卖者被称为价格 接受者。 Buyers and sellers in competitive markets are said to be price takers. 5 竞争企业的收益 Revenue of a Competitive Firm 企业的总收益是销售价格乘以销售量。 Total revenue for a firm is the selling price times the quantity sold. TR = (P X Q) 6 竞争企业的收益 Revenue of a Competitive Firm 总收益与产量成比例。 Total revenue is proportional to the amount of output
竞争企业的收益 竞争企业的收益 Revenue of a Competitive Firm Revenue of a Competitive Firm 对所有企业来说,平均收益等于物品的价格。 平均收益告诉我们一个企业从每一典型单 For all firms, average revenue equals the 位的销售中得到多少收益 price of the good Average revenue tells us how much revenue a firm receives for the typical Total revenu unit sold (Price x Quantity) Price 竞争企业的收益 竞争企业的收益 Revenue of a competitive Firm Revenue of a Competitive Firm 边际收益是销售量增加一个单位带来的总 收益的变化。 对竞争企业来说,边际收益等于物品价格。 Marginal revenue is the change in total For competitive firms, marginal revenue revenue from an additional unit sold equals the price of the good MR=△TR/△Q 竞争企业的总收益、平均收益和边际收益 竞争企业的利润最大化 Total, Average, and Marginal Revenue Profit maximization for the for a Competitive Firm Competitive Firm ◆竞争企业的目标是利润最大化 The goal of a competitive firm is to maximize 价格 Price Revenu profit. ◆这意味着企业将生产使总收益和总成本之差 最大的产量 This means that the firm will want to produce the quantity that maximizes the difference between total revenue and total cost
2 7 竞争企业的收益 Revenue of a Competitive Firm 平均收益告诉我们一个企业从每一典型单 位的销售中得到多少收益。 Average revenue tells us how much revenue a firm receives for the typical unit sold. 8 竞争企业的收益 Revenue of a Competitive Firm 对所有企业来说，平均收益等于物品的价格。 For all firms, average revenue equals the price of the good. Average revenue = Total revenue Quantity = (Price Quantity) Quantity = Price × 9 竞争企业的收益 Revenue of a Competitive Firm 边际收益是销售量增加一个单位带来的总 收益的变化。 Marginal revenue is the change in total revenue from an additional unit sold. MR =∆TR/ ∆Q 10 竞争企业的收益 Revenue of a Competitive Firm 对竞争企业来说，边际收益等于物品价格。 For competitive firms, marginal revenue equals the price of the good. 11 竞争企业的总收益、平均收益和边际收益 Total, Average, and Marginal Revenue for a Competitive Firm 产量Quanti ty (Q) 价格Price (P) 总收益Total Revenue (TR=PxQ) 平均收益Average Revenue (AR=TR/Q) 边际收益Marginal Revenue (MR= ) 1 $6.00 $6.00 $6.00 2 $6.00 $12.00 $6.00 $6.00 3 $6.00 $18.00 $6.00 $6.00 4 $6.00 $24.00 $6.00 $6.00 5 $6.00 $30.00 $6.00 $6.00 6 $6.00 $36.00 $6.00 $6.00 7 $6.00 $42.00 $6.00 $6.00 8 $6.00 $48.00 $6.00 $6.00 ∆TR/ ∆Q 12 竞争企业的利润最大化 Profit Maximization for the Competitive Firm 竞争企业的目标是利润最大化。 The goal of a competitive firm is to maximize profit. 这意味着企业将生产使总收益和总成本之差 最大的产量。 This means that the firm will want to produce the quantity that maximizes the difference between total revenue and total cost
利润最大化:一个数字例子 竞争企业的利海最大化 Profit Maximization Profit Maximization for the Competitive Firm A Numerical Example 本中致签盐搞 格产量Qam基敏l 竞争企业的利润最大化 竞争企业的利润最大化 Profit maximization for the Profit maximization for the Competitive Firm Competitive Firm 在利润最大化的产量水平上,边 当 When Mr>MC增加 ncrease G 际收益和边际成本正好相等。 Profit maximization occurs at the 当 When MR<MC减少 decrease g quantity where marginal revenue equals marginal cost. 当 When MR=MC利润是最大 的 Profit is maximized 边际成本曲线和企业的供给曲线 边际成本的线和企业的供给曲线 The Marginal-Cost Curve and the The Marginal-Cost Curve and the Firm's Supply Decision Firm's Supply Decision 由于企业的边际成本曲线决定了企业 在任何一种价格时愿意供给多少,因 the firms supply 此,这就是竞争企业的供给曲线 ATC Because the firm's marginal-cost curve determines how much the firm Avc is willing to supply at any price, it the competitive firms supply curve
3 13 利润最大化：一个数字例子 Profit Maximization: A Numerical Example 价格Pric e (P) 产量Quanti ty (Q) 总收益Total Revenue (TR=PxQ) 总成本Total Cost (TC) 利润Profit (TR-TC) 边际收益Marginal Revenue (MR= ) 边际成本Margi nal Cost MC= 0 $0.00 $3.00 -$3.00 $6.00 1 $6.00 $5.00 $1.00 $6.00 $2.00 $6.00 2 $12.00 $8.00 $4.00 $6.00 $3.00 $6.00 3 $18.00 $12.00 $6.00 $6.00 $4.00 $6.00 4 $24.00 $17.00 $7.00 $6.00 $5.00 $6.00 5 $30.00 $23.00 $7.00 $6.00 $6.00 $6.00 6 $36.00 $30.00 $6.00 $6.00 $7.00 $6.00 7 $42.00 $38.00 $4.00 $6.00 $8.00 $6.00 8 $48.00 $47.00 $1.00 $6.00 $9.00 ∆TR/ ∆Q ∆TC / ∆Q P=MR1 P = AR = MR MC 竞争企业的利润最大化 Profit Maximization for the Competitive Firm 产量Quantity 0 成本Costs and 收益Revenue ATC AVC QMAX 通过生产边际成本等于边际 收益的产量，企业使利润最 大化 The firm maximizes profit by producing the quantity at which marginal cost equals marginal revenue. MC1 Q1 MC2 Q2 15 竞争企业的利润最大化 Profit Maximization for the Competitive Firm 在利润最大化的产量水平上，边 际收益和边际成本正好相等。 Profit maximization occurs at the quantity where marginal revenue equals marginal cost. 16 竞争企业的利润最大化 Profit Maximization for the Competitive Firm 当When MR > MC 增加increase Q 当When MR < MC 减少decrease Q 当When MR = MC 利润是最大 的Profit is maximized. 17 边际成本曲线和企业的供给曲线 The Marginal-Cost Curve and the Firm’s Supply Decision... 由于企业的边际成本曲线决定了企业 在任何一种价格时愿意供给多少，因 此，这就是竞争企业的供给曲线。 Because the firm’s marginal-cost curve determines how much the firm is willing to supply at any price, it is the competitive firm’s supply curve. 边际成本曲线和企业的供给曲线 The Marginal-Cost Curve and the Firm’s Supply Decision... 0 Quantity Costs and Revenue MC ATC AVC Q1 P1 P2 Q2 这部分的企业边际成本曲 线也是企业的供给曲线 This section of the firm’s MC curve is also the firm’s supply curve
企业的短期停业决策 企业的短期停业决策 The Firm's short-Run Decision The Firm's Short-Run Decision to shut down to shut down ◆停止营业指在某个特定时期,由于当前 的市场条件而不生产任何东西的短期决 ◆当企业决定退出时,它考虑固定成本 固 但当企业决定是否停业时,它不考虑 A shutdown refers to a short-run decision The firm considers its fixed costs when not to produce anything during a specific riod of time because of current market deciding to exit, but ignores them when conditions deciding whether to shut down. ◆退出指高开市场的长期决策。 ◆当做出是否停业的短期决策时,固定 Exit refers to a long-run decision to leave the market 企业的短期停业决策 企业的短期停业决策 The Firm's Short-Run Decision The Firm's short-Run Decision to shut down to shut down ◆沉没成本是那些已经发生而且无法回收 如果生产得到的收益小于生产的可变成 的成本。 本时,企业就停止营业。 Sunk costs are costs that have The firm shuts down if the revenue it gets already been committed and cannot from producing is less than the variable be recovered cost of production. 在某种意义上说,沉没成本是机会成本 如果TR<vc,停业( hut down if TR<vc) 的反面:无论你做什么选择,沉没成本 如果TRQ<vcQ,〃业( Shut down If TR/Q<vcQ) 不可避免 如果P<AVC,件业( Shut down ifP<Avc) 企业的短期业决袋 The firm's short-Run Decision to shut Down 企业的短期停业决策 The Firm's Short-Run Decision 企业的供始曲端 to shut down 竞争企业短期供给曲线是边际成本曲线 在平均可变成本曲线以上的那一部分 a profit. The portion of the marginal-cost curve the short the competitive firms short-run supply curve shut down
4 19 企业的短期停业决策 The Firm’s Short-Run Decision to Shut Down 停止营业指在某个特定时期，由于当前 的市场条件而不生产任何东西的短期决 策。 A shutdown refers to a short-run decision not to produce anything during a specific period of time because of current market conditions. 退出指离开市场的长期决策。 Exit refers to a long-run decision to leave the market. 20 企业的短期停业决策 The Firm’s Short-Run Decision to Shut Down 当企业决定退出时，它考虑固定成本 ，但当企业决定是否停业时，它不考虑 固定成本。 The firm considers its fixed costs when deciding to exit, but ignores them when deciding whether to shut down. 当做出是否停业的短期决策时，固定 成本被称为沉没成本。 21 企业的短期停业决策 The Firm’s Short-Run Decision to Shut Down 沉没成本是那些已经发生而且无法回收 的成本。 Sunk costs are costs that have already been committed and cannot be recovered. 在某种意义上说，沉没成本是机会成本 的反面：无论你做什么选择，沉没成本 不可避免。 22 企业的短期停业决策 The Firm’s Short-Run Decision to Shut Down 如果生产得到的收益小于生产的可变成 本时，企业就停止营业。 The firm shuts down if the revenue it gets from producing is less than the variable cost of production. 如果TR AVC， 短期内继续生产 If P > AVC, keep producing in the short run. 如果P > ATC ， 继续生产，有利润 If P > ATC, keep producing at a profit. 企业的短期供给曲线 Firm’s short-run supply curve. 24 企业的短期停业决策 The Firm’s Short-Run Decision to Shut Down 竞争企业短期供给曲线是边际成本曲线 在平均可变成本曲线以上的那一部分。 The portion of the marginal-cost curve that lies above average variable cost is the competitive firm’s short-run supply curve
企业进入或退出市场的长期决策 企业进入或退出市场的长期决策 The Firm' s Long-Run Decision to The Firm's Long- Run Decision to Exit or enter a market Exit or Enter a Market t在的成果处非速到的收益将小于 ◆如果有利可图,企业就将进入这一市场。 A firm will enter the industry if such an In the long-run, the firm exits if the revenue it would get from producing is less than its action would be profitable total cost 如果TR>TC,进λ( Enter if TR>Tc) 如果TRTcQ,进入( Enter if TR/Q>TcQ) 如果TRQATC,进入( Enter if P>ATC) 如果PATc ATC 成本曲线位于平均总成本曲线之 上的那一部分 The competitive firms long-run supply curve is the portion of its marginal-cost curve that lies 数 rQuantity above average total cost. 企业的短期和长期供给曲线 用图形来衡量竞争企业的利胸 The Firm's short-Run and Measuring Profit in the Graph for Long- Run Supply Curves the Competitive Firr a.有利润的企业 ◆短期供给曲线 Short-Run Supply Curve A Firm with Profits ◆边际成本曲线在平均可变成本曲线以上的那一部 ATC The portion of its marginal cost curve that lies P =AR==M above average variable cost. ◆长期供给曲线 Long-Run Supply Curve ◆边际成本曲线在平均总成本曲线最低点以上的那 The marginal cost curve above the minimum point of its average total cost curve
5 25 企业进入或退出市场的长期决策 The Firm’s Long-Run Decision to Exit or Enter a Market 在长期，如果从生产中得到的收益将小于 它的总成本，企业就退出。 In the long-run, the firm exits if the revenue it would get from producing is less than its total cost. 如果TR TC ，进入 (Enter if TR > TC) 如果TR/Q > TC/Q ，进入 (Enter if TR/Q > TC/Q) 如果P > ATC，进入 (Enter if P > ATC) 27 竞争企业的长期供给曲线 The Competitive Firm’s LongRun Supply Curve... 数量Quantity MC ATC 0 成本 Costs 如果P > ATC ，企业进入 Firm enters if P > ATC 如果P < ATC，企业 退出 Firm exits if P < ATC 企业的长期供给曲 线Firm’s longrun supply curve 28 竞争企业的长期供给曲线 The Competitive Firm’s LongRun Supply Curve 竞争企业的长期供给曲线是边际 成本曲线位于平均总成本曲线之 上的那一部分。 The competitive firm’s long-run supply curve is the portion of its marginal-cost curve that lies above average total cost. 29 企业的短期和长期供给曲线 The Firm’s Short-Run and Long-Run Supply Curves 短期供给曲线Short-Run Supply Curve 边际成本曲线在平均可变成本曲线以上的那一部 分。 The portion of its marginal cost curve that lies above average variable cost. 长期供给曲线Long-Run Supply Curve 边际成本曲线在平均总成本曲线最低点以上的那 一部分。 The marginal cost curve above the minimum point of its average total cost curve. 30 利润Profit Q 用图形来衡量竞争企业的利润 Measuring Profit in the Graph for the Competitive Firm... 0 Quantity Price P = AR = MR MC ATC P ATC 利润最大化产量 Profit-maximizing quantity a. 有利润的企业 A Firm with Profits
用图形来衡量竞争企业的利 measuring Profit in the Graph for the competitive Firm 竞争市场中的供给 有员企业 A Firm with Losses Supply in a Competitive Market 市场供给等于市场中各个企业 供给量的总和。 P = ARE MR Market supply equals the sum of the quantities supplied by the individual firms in the market mm小化m 短期:有固定数目企业的市场 短期:有固定数目企业的市场 The Short Run: Market Supply The Short Run: Market Supply with a Fixed number of firms with a Fixed number of firms ◆在任何一种既定价格上,每个企业供给 个删鱼业 使边际成本等于价格的产量。 dual Firm Supply For any given price, each firm supplies a Supply quantity of output so that its marginal cost equals price. s2.00 来线给曲线反应了个别企业的边际成 The market supply curve reflects the individual firms'marginal cost curves 100,000200000 (firm) 长期:有进入和退出的市场供给 长期:有进入和退出的市场供给 The Long Run: Market Supply The Long Run: Market Supply with Entry and Exit with Entry and Exit ◆企业将进入或退出市场,直到利润被推向零。 m's Zero-profit Condition Firms will enter or exit the market until profit is driven to zero ◆在长期,价格等于平均总成本的最小值。 In the long run, price equals the minimum of average total cost. ◆长期市场供给曲线是一条在此价格上的水平线 The long- run market supply curve is horizonta at this price. (firm
6 31 亏损 Loss 用图形来衡量竞争企业的利润 Measuring Profit in the Graph for the Competitive Firm... 0 Quantity Price P = AR = MR MC ATC P Q 亏损最小化产量 Loss-minimizing quantity ATC b. 有亏损企业 A Firm with Losses 32 竞争市场中的供给 Supply in a Competitive Market 市场供给等于市场中各个企业 供给量的总和。 Market supply equals the sum of the quantities supplied by the individual firms in the market. 33 短期：有固定数目企业的市场 The Short Run: Market Supply with a Fixed Number of Firms 在任何一种既定价格上，每个企业供给 使边际成本等于价格的产量。 For any given price, each firm supplies a quantity of output so that its marginal cost equals price. 市场供给曲线反应了个别企业的边际成 本曲线。 The market supply curve reflects the individual firms’ marginal cost curves. 34 短期：有固定数目企业的市场 The Short Run: Market Supply with a Fixed Number of Firms... (a) 个别企业供给 Individual Firm Supply Quantity (firm) 0 Price (b) 市场供给 Market Supply Quantity (market) Price 0 MC Supply 1.00 $2.00 100 200 1.00 $2.00 100,000 200,000 35 长期：有进入和退出的市场供给 The Long Run: Market Supply with Entry and Exit 企业将进入或退出市场，直到利润被推向零。 Firms will enter or exit the market until profit is driven to zero. 在长期，价格等于平均总成本的最小值。 In the long run, price equals the minimum of average total cost. 长期市场供给曲线是一条在此价格上的水平线 The long-run market supply curve is horizontal at this price. 36 长期：有进入和退出的市场供给 The Long Run: Market Supply with Entry and Exit... (a) 企业的零利润条件 Firm’s Zero-Profit Condition 数量（企业） Quantity (firm) 0 价格 Price P = ATC的最小值 P = minimum ATC (b) 市场供给 Market Supply 数量（市场） Quantity (market) 价格 Price 0 供给 Supply MC ATC
长期:有进入和退出的市场供给 为什么企业获得零利润还在经营? The Long Run: Market Supply Why Firms Stay in Business with Entry and Exit with Zero Profit? 程结束是,仍然留在市场中的企 ◆利润等于总收益减总成本。 Profit equals total revenue minus total cost. t the end of the process of entry and exit, firms that remain must be making zero economie profit. ◆总成本包括企业的所有机会成本。 Total cost includes all the opportunity costs of the firm. ◆是意学效与平均总成本被推向相时,进入与遇出 在零利润均衡时,企业的收益应该补偿所有者用于使 The process of entry exit ends only when price and average total cost are driven to equality In the zero-profit equilibrium, the firms revenue ◆竞争市场长期均衡一定是企业在其有效规模点运行 mpensates the owners for the time and money they Long- run equilibrium must have firms operating at ep the b their efficient seale ◆经济利润不同于会计利润 Economic profits differ from accounting profits. 需求的增加在短期内的影响 需求的增加在短期内和长期内的影响 Increase in Demand in the Increase in Demand in the short Run Short Run d(轴hnR ◆需求的增加在短期内提高价格并增加 An increase in demand raises price and quantity in the short run. ◆企业赚到正利润,因为价格现在高于 AN 长期供给 Firms earn profits because price now exceeds average total cost. 需求的增加在短期内和长期内的影响1「求的增加在短期内和长期内 Increase in Demand in the short run Increase in Demand in the short run and in the long run and in the Long Run (c)长期反应ong Frm企业 市场 Market 企业Fm Response 利润Pro 长期供给 金出H30器me 41
7 37 长期：有进入和退出的市场供给 The Long Run: Market Supply with Entry and Exit 当这种进入和退出过程结束是，仍然留在市场中的企 业必定得到零经济利润。 At the end of the process of entry and exit, firms that remain must be making zero economic profit. 只有当价格与平均总成本被推向相等时，进入与退出 过程才结束。 The process of entry & exit ends only when price and average total cost are driven to equality. 竞争市场长期均衡一定是企业在其有效规模点运行。 Long-run equilibrium must have firms operating at their efficient scale. 38 为什么企业获得零利润还在经营？ Why Firms Stay in Business with Zero Profit? 利润等于总收益减总成本。 Profit equals total revenue minus total cost. 总成本包括企业的所有机会成本。 Total cost includes all the opportunity costs of the firm. 在零利润均衡时，企业的收益应该补偿所有者用于使 企业维持的时间和金钱。 In the zero-profit equilibrium, the firm’s revenue compensates the owners for the time and money they expend to keep the business going. 经济利润不同于会计利润。 Economic profits differ from accounting profits. 39 需求的增加在短期内的影响 Increase in Demand in the Short Run 需求的增加在短期内提高价格并增加 数量。 An increase in demand raises price and quantity in the short run. 企业赚到正利润，因为价格现在高于 平均总成本。 Firms earn profits because price now exceeds average total cost. 40 需求的增加在短期内和长期内的影响 Increase in Demand in the Short Run and in the Long Run 企业Firm 市场Market Quantity (企业firm) 0 Price MC ATC P1 Quantity (市场market) Price 0 D1 P1 Q1 A S1 长期供给 Long-run supply (a)初始条件Initial Condition P 41 D2 需求的增加在短期内和长期内的影响 Increase in Demand in the Short Run and in the Long Run Firm企业 市场Market Quantity (企业firm) 0 Price MC ATC P1 Quantity (市场market) Price 0 D1 P1 Q1 A S1 长期供给 Long-run supply (b) 短期反应Short-Run Response Q2 B P2 P2 利润Profit 42 需求的增加在短期内和长期内的影响 Increase in Demand in the Short Run and in the Long Run 企业Firm 市场Market Quantity (firm) 0 Price MC ATC P1 Quantity (market) Price 0 D1 P1 Q1 A S1 长期供给 Long-run supply (c) 长期反应Long-Run Response D2 B Q2 P2 S2 C Q3
为什么长期供给曲线会向右上方倾斜 Why the Long-Run Supply Curve 边际企业 Might Slope Upward Marginal Firm 些用于生产的资源数量可能是有限 边际企业是如果价格有任何下 Some resources used in production 降就退出市场的企业。 nay be available only in limited quantities The marginal firm is the firm ◆企业可能有不同的成本 that would exit the market if the Firms may have different costs price were any lower 总结 总结 Summary Summary ◆由于竞争企业是价格接受者,所以它的 ◆为了利润最大化,企业选择使边际收益等于边 收益与产 比例的。 To maximize profit a firm chooses the quantity Because a competitive firm is a price of output such that marginal revenue equals taker, its revenue is proportional to the marginal cost. amount of output it produces. ◆这也是使价格等于边际成本的产量。 ◆物品的价格等于企业的平均收益和边际 This is also the quantity at which price equals 收益 The price of the good equals both the ◆因此,企业的边际成本曲线是它的 firm's average revenue and its marginal Therefore, the firms marginal cost curve is its revenue supply curve. 总结 总结 Summary Summary °尔到毕均弯发同支翔宠牌在智墨物品价 ◆在有自由进入与退出的市场上,长期中企业利 润为零,所有企业在有效规模点生产。 In the short run when a firm cannot recover its fixed costs, the firm will choose to shut down In a market with free entry and exit, profits are mporarily if the price of the good is less than driven to zero in the long run and all firms average variable cost. produce at the efficient scale. ◆在长期中,企业能够回收其固定和可变成本,如果 ◆需求变动在不同时间范围之内有不同影响。 Changes in demand have different effects over In the long run when the firm can recover both different time he ron fixed and variable costs. it will choose to exit if the price is less than average total cost
8 43 为什么长期供给曲线会向右上方倾斜 Why the Long-Run Supply Curve Might Slope Upward 一些用于生产的资源数量可能是有限 的。 Some resources used in production may be available only in limited quantities. 企业可能有不同的成本。 Firms may have different costs. 44 边际企业 Marginal Firm 边际企业是如果价格有任何下 降就退出市场的企业。 The marginal firm is the firm that would exit the market if the price were any lower. 45 总结 Summary 由于竞争企业是价格接受者，所以它的 收益与产量是同比例的。 Because a competitive firm is a price taker, its revenue is proportional to the amount of output it produces. 物品的价格等于企业的平均收益和边际 收益。 The price of the good equals both the firm’s average revenue and its marginal revenue. 46 总结 Summary 为了利润最大化，企业选择使边际收益等于边 际成本的产量。 To maximize profit a firm chooses the quantity of output such that marginal revenue equals marginal cost. 这也是使价格等于边际成本的产量。 This is also the quantity at which price equals marginal cost. 因此，企业的边际成本曲线是它的供给曲线。 Therefore, the firm’s marginal cost curve is its supply curve. 47 总结 Summary 在短期中，企业不能回收其固定成本，如果物品价 格小于平均可变成本，企业将选择停止营业。 In the short run when a firm cannot recover its fixed costs, the firm will choose to shut down temporarily if the price of the good is less than average variable cost. 在长期中，企业能够回收其固定和可变成本，如果 价格小于平均总成本，企业将选择退出。 In the long run when the firm can recover both fixed and variable costs, it will choose to exit if the price is less than average total cost. 48 总结 Summary 在有自由进入与退出的市场上，长期中企业利 润为零，所有企业在有效规模点生产。 In a market with free entry and exit, profits are driven to zero in the long run and all firms produce at the efficient scale. 需求变动在不同时间范围之内有不同影响。 Changes in demand have different effects over different time horizons