📚 AP Microeconomics: Key Concepts, Formulas, and Practice Questions | AP微观经济：知识点梳理与公式例题详解
Welcome to our comprehensive AP Microeconomics revision guide. This article breaks down the core principles you need to master, from supply and demand to market failure. Each section combines clear explanations with essential formulas and worked examples, helping you build both conceptual understanding and problem-solving skills. Whether you are aiming for a perfect score or just getting started, this resource is designed to be your one-stop study companion.
欢迎阅读我们全面的AP微观经济学复习指南。本文梳理了你必须掌握的核心原理，从供需到市场失灵。每个部分都将清晰的解释与关键公式和典型例题相结合，帮助你建立概念理解与解题能力。无论你的目标是满分还是刚刚起步，这份资料都旨在成为你的一站式学习伙伴。
1. Demand and Supply | 需求与供给
Demand represents the quantity of a good consumers are willing and able to buy at various prices, holding other factors constant. The law of demand states that as price rises, quantity demanded falls, ceteris paribus. Supply represents the quantity producers are willing and able to sell at various prices. The law of supply states that as price rises, quantity supplied rises. Equilibrium occurs where quantity demanded equals quantity supplied. Shifts in demand or supply change equilibrium price and quantity.
需求表示在其他因素不变的情况下，消费者愿意并且能够购买的某种商品的数量。需求定律指出，在其他条件不变时，价格上升，需求量下降。供给表示生产者在不同价格下愿意且能够销售的数量。供给定律指出，价格上升，供给量上升。均衡发生在需求量等于供给量之处。需求或供给的移动会改变均衡价格和数量。
y shifters of demand include income, tastes, prices of related goods, expectations, and number of buyers. Supply shifters include input prices, technology, number of sellers, and expectations. A rightward shift of demand increases both equilibrium price and quantity; a rightward shift of supply lowers price and raises quantity.
需求函数可写作 Qd = a - bP，供给函数为 Qs = c + dP。均衡通过令 Qd = Qs 求得。需求的主要移动因素包括收入、偏好、相关商品价格、预期和买家数量。供给的移动因素包括投入品价格、技术、卖家数量和预期。需求右移会同时提高均衡价格和数量；供给右移会降低价格并提高数量。
- 2P = -20 + 4P → 120 = 6P → P = 20. Then Q = 100 - 2(20) = 60. If demand increases to Qd' = 140 - 2P, the new equilibrium: 140 - 2P = -20 + 4P → 160 = 6P → P ≈ 26.67, Q ≈ 86.67.
例题：假设 Qd = 100 - 2P，Qs = -20 + 4P。求均衡价格和数量。令 100 - 2P = -20 + 4P → 120 = 6P → P = 20。则 Q = 100 - 2(20) = 60。如果需求增加到 Qd' = 140 - 2P，新的均衡：140 - 2P = -20 + 4P → 160 = 6P → P ≈ 26.67，Q ≈ 86.67。
2. Elasticity | 弹性
s how much one variable responds to changes in another. Price elasticity of demand (PED) = % change in quantity demanded / % g the midpoint method: PED = [(Q2 - Q1) / ((Q1 + Q2)/2)] / [(P2 - P1) / ((P1 + P2)/2)]. If |PED| > 1, demand is elastic; if |PED| rice decrease raises total revenue; when inelastic, a price decrease lowers total revenue.
弹性衡量一个变量对另一个变量变化的反应程度。需求的价格弹性（PED）= 需求量变动百分比 / 价格变动百分比。采用中点法：PED = [(Q2 - Q1) / ((Q1 + Q2)/2)] / [(P2 - P1) / ((P1 + P2)/2)]。若 |PED| > 1，需求富有弹性；若 |PED| < 1，缺乏弹性；若 = 1，单位弹性。总收益检验：当需求富有弹性时，降价会增加总收益；缺乏弹性时，降价会减少总收益。
Income elasticity of demand (YED) = % change in quantity demanded / % e positive YED; inferior goods have negative YED. Cross-price elasticity of demand (XED) = % change in quantity demanded of good A / % indicates substitutes; negative indicates complements. Price elasticity of supply (PES) = % change in quantity supplied / % change in price.
需求的收入弹性（YED）= 需求量变动百分比 / 收入变动百分比。正常品YED为正；低档品YED为负。需求的交叉价格弹性（XED）= 商品A需求量变动百分比 / 商品B价格变动百分比。XED为正表示替代品；负表示互补品。供给的价格弹性（PES）= 供给量变动百分比 / 价格变动百分比。
Example: Price of coffee rises from $2 to $2.50, and quantity demanded falls from 100 to 80 cups. Using midpoint method: %ΔQ = (80-100)/((100+80)/2) = -20/90 ≈ -22.2%. %ΔP = (2.5-2)/((2+2.5)/2) = 0.5/2.25 ≈ 22.2%. PED = -22.2%/22.2% = -1. Unit elastic. Total revenue at original price = $200; at new price = $2.5 × 80 = $200, unchanged.
例题：咖啡价格从$2涨到$2.50，需求量从100杯降到80杯。中点法：%ΔQ = (80-100)/((100+80)/2) = -20/90 ≈ -22.2%。%ΔP = (2.5-2)/((2+2.5)/2) = 0.5/2.25 ≈ 22.2%。PED = -22.2%/22.2% = -1，单位弹性。原总收益 = $200；新价格下 = $2.5 × 80 = $200，不变。
3. Government Intervention: Price Controls and Taxes | 政府干预：价格控制与税收
Price ceilings are legal maximum prices set below equilibrium, causing shortages. Price floors are legal minimum prices set above equilibrium, causing surpluses. Taxes shift the supply curve upward by the amount of the tax. The incidence of a tax depends on relative elasticities of demand and supply; the more inelastic side bears a greater burden. Subsidies shift the supply curve downward, lowering market price and increasing quantity.
价格上限是设定在均衡价格之下的法定最高价格，会导致短缺。价格下限是设定在均衡价格之上的法定最低价格，会导致过剩。税收使供给曲线向上移动税额的量。税收负担取决于需求和供给的相对弹性；越缺乏弹性的一方承担的税负越大。补贴使供给曲线向下移动，降低市场价格并增加数量。
× tax × (Q0 - Qt), where Q0 is equilibrium quantity without tax, Qt is quantity after tax. Consumer surplus, producer surplus, and tax revenue are affected.
税收收入 = 税额 × 税后销售量。无谓损失（DWL）是因市场扭曲而导致的总剩余损失。对于从量税，DWL = 0.5 × 税额 × (Q0 - Qt)，其中Q0为无税均衡数量，Qt为税后数量。消费者剩余、生产者剩余和税收收入均受到影响。
100 - 2P, Qs = -20 + 2P. Equilibrium P = 30, Q = 40. Government imposes a price ceiling of $20. Qd = 100 - 40 = 60, Qs = -20 + 40 = 20. Shortage = 40 units. If a tax of $ P → 140 = 4P → P = 35 (price buyers pay). Sellers receive 25. Quantity = 30. Tax revenue = $10 × 30 = $300.
例题：某市场 Qd = 100 - 2P，Qs = -20 + 2P。均衡 P = 30，Q = 40。政府实施$20的价格上限。Qd = 60，Qs = 20，短缺40单位。若征收每单位$10的税，新供给：Qs = -20 + 2(P - 10) = -40 + 2P。新均衡：100 - 2P = -40 + 2P → 140 = 4P → P = 35（买方支付价），卖方实收25。数量 = 30。税收收入 = $10 × 30 = $300。
4. Consumer Choice Theory | 消费者选择理论
e additional utility from one more unit. The law of diminishing marginal utility states that as more of a good is consumed, the marginal utility decreases. The optimal consumption rule: MUx/Px = MUy/Py. If this equality does not hold, the consumer should reallocate spending to the good with higher marginal utility per dollar.
消费者旨在在预算约束下最大化效用。总效用是消费带来的满足感；边际效用（MU）是多消费一单位所带来的额外效用。边际效用递减规律指出，随着某种商品消费量的增加，边际效用递减。最优消费法则：MUx/Px = MUy/Py。如果不相等，消费者就应将支出重新分配到单位货币边际效用更高的商品上。
mbinations giving the same total utility. MRS (marginal rate of substitution) = MUx/MUy. Optimal bundle is where the highest indifference curve is tangent to the budget line, so MRS = Px/Py.
预算线表示花光全部收入的两种商品的所有组合：收入 = Px·X + Py·Y。斜率为 -Px/Py。无差异曲线代表产生相同总效用的组合。边际替代率（MRS）= MUx/MUy。最优消费束位于无差异曲线与预算线相切之处，因此 MRS = Px/Py。
Example: Amy has $20 to spend on apples (A) at $2 each and bananas (B) at $ 0 + A. Budget: 2A + 1B = 20. Substitute: 2A + 10 + A = 20 → 3A = 10 → A ≈ 3.33, B ≈ 13.33.
例题：艾米有$20购买苹果（A，每个$2）和香蕉（B，每个$1）。她的 MUa = 20 - A，MUb = 15 - 0.5B。最优条件：MUa/Pa = MUb/Pb → (20 - A)/2 = (15 - 0.5B)/1 → 20 - A = 30 - B → B = 10 + A。预算：2A + 1B = 20。代入得 2A + 10 + A = 20 → 3A = 10 → A ≈ 3.33，B ≈ 13.33。
5. Production and Costs | 生产与成本
o diminishing marginal returns. Marginal product (MP) is the change in TP from hiring one more unit of variable input. Costs include fixed costs (FC), variable costs (VC), and total cost (TC) = FC + VC. Average total cost (ATC) = TC/Q; average variable cost (AVC) = VC/Q; average fixed cost (AFC) = FC/Q. Marginal cost (MC) = ΔTC/ΔQ. The MC curve intersects AVC and ATC at their minimum points.
在短期中，至少一种生产要素是固定的。总产量（TP）起初以递增速率上升，随后因边际报酬递减而以递减速率上升。边际产量（MP）是增加一单位可变投入所带来的总产量变动。成本包括固定成本（FC）、可变成本（VC）和总成本（TC）= FC + VC。平均总成本（ATC）= TC/Q；平均可变成本（AVC）= VC/Q；平均固定成本（AFC）= FC/Q。边际成本（MC）= ΔTC/ΔQ。MC曲线与AVC和ATC曲线相交于它们的最低点。
The shape of cost curves is determined by production function. When MP is rising, MC is falling; when MP is falling, MC is rising. The long-run average total cost (LRATC) reflects all inputs variable. Economies of scale occur when LRATC declines as output increases; diseconomies when LRATC rises; constant returns to scale when LRATC is flat.
成本曲线的形状由生产函数决定。当MP上升时，MC下降；当MP下降时，MC上升。长期平均总成本（LRATC）反映所有投入均可变的情况。当产出增加时LRATC下降，即为规模经济；LRATC上升则为规模不经济；LRATC平坦则为规模报酬不变。
Example: A firm' 10Q + 2Q²)/Q = 200/Q + 10 + 2Q = 20 + 10 + 20 = 50. At Q=10, ATC = MC = 50, indicating minimum ATC.
例题：某企业的总成本函数为 TC = 200 + 10Q + 2Q²。求 Q=10 时的 MC、AVC 和 ATC。MC = dTC/dQ = 10 + 4Q = 10 + 40 = 50。AVC = (10Q + 2Q²)/Q = 10 + 2Q = 10 + 20 = 30。ATC = (200 + 10Q + 2Q²)/Q = 200/Q + 10 + 2Q = 20 + 10 + 20 = 50。当 Q=10 时，ATC = MC = 50，表明处于ATC最低点。
6. Perfect Competition | 完全竞争
ers, facing a horizontal demand curve at the market price. In the short run, the firm maximizes profit where MR = MC, with MR = P. Economic profit = (P - ATC) × Q. If P > ATC, firm earns positive profit; if P = ATC, zero economic profit (normal profit); if P < ATC, loss. The firm will shut down if P < AVC.
完全竞争市场拥有无数买家和卖家、同质产品、自由进出和充分信息。企业是价格接受者，面临一条在市场价格处的水平需求曲线。在短期，企业在 MR = MC 处实现利润最大化，且 MR = P。经济利润 = (P - ATC) × Q。若 P > ATC，企业获得正利润；若 P = ATC，零经济利润（正常利润）；若 P < ATC，亏损。如果 P < AVC，企业将停产。
C, and economic profit becomes zero. If firms are making losses, some exit, reducing supply, raising price until P = min ATC. Therefore, long-run equilibrium occurs at P = MC = min ATC, achieving both productive and allocative efficiency.
在长期，企业可以进出市场。如果企业正在盈利，新企业进入，增加市场供给，降低价格，直至 P = 最低ATC，经济利润降至零。如果企业亏损，部分退出，减少供给，提高价格，直至 P = 最低ATC。因此，长期均衡发生在 P = MC = min ATC，同时实现生产效率和配置效率。
Example: A perfectly competitive firm's cost curves: MC = 4Q, ATC = 2Q + 50/Q. Market price is $ ing Q: MR = MC → 40 = 4Q → Q = 10. Profit = TR - TC = (40×10) - (2×100 + 50) = 400 - 250 = $ 5), firm earns positive economic profit. In the long run, entry will wipe out this profit.
例题：某完全竞争企业的成本曲线：MC = 4Q，ATC = 2Q + 50/Q。市场价格为$40。利润最大化产量：MR = MC → 40 = 4Q → Q = 10。利润 = TR - TC = (40×10) - (2×100 + 50) = 400 - 250 = $150。因 P > ATC（Q=10时 ATC=25），企业获得正经济利润。长期中，新企业进入将使该利润消失。
7. Monopoly | 垄断
and curve. To sell more, the monopolist must lower price, so marginal revenue (MR) lies below demand. Profit maximization occurs at MR = MC. The monopolist then sets price from the demand curve at that quantity. Monopolies create deadweight loss because price exceeds marginal cost, leading to underproduction compared to perfect competition. Price discrimination can convert some consumer surplus into profit and may reduce DWL if perfect discrimination occurs.
垄断是指只有一个卖家、没有近似替代品且进入壁垒很高的市场。垄断者面临向下倾斜的市场需求曲线。为增加销量，垄断者必须降价，因此边际收益（MR）位于需求曲线下方。利润最大化发生在 MR = MC 处。然后垄断者根据该产量在需求曲线上确定价格。垄断会造成无谓损失，因为价格高于边际成本，导致与完全竞争相比产量不足。价格歧视可将部分消费者剩余转化为利润，如果实行完全歧视，可能减少无谓损失。
poly occurs when economies of scale make one firm more efficient than multiple firms. Governments may regulate monopolies through price caps at MC or average cost pricing.
对于线性需求 P = a - bQ，MR = a - 2bQ。利润 = TR - TC = P×Q - TC。垄断势力常用勒纳指数衡量：(P - MC)/P = -1/PED。当规模经济使一家企业比多家企业更有效率时，产生自然垄断。政府可通过边际成本定价或平均成本定价的价格上限来管制垄断。
e outcome (P=MC): 100 - Q = 20 → Q = 80, P = 20. DWL = 0.5 × (60 - 20) × (80 - 40) = 0.5 × 40 × 40 = 800.
例题：需求：P = 100 - Q，TC = 20Q。MR = 100 - 2Q，MC = 20。MR = MC：100 - 2Q = 20 → Q = 40。价格 = 100 - 40 = 60。利润 = 60×40 - 20×40 = 1600。完全竞争结果（P=MC）：100 - Q = 20 → Q = 80，P = 20。DWL = 0.5 × (60 - 20) × (80 - 40) = 0.5 × 40 × 40 = 800。
8. Monopolistic Competition and Oligopoly | 垄断竞争与寡头
Monopolistic competition has many firms, differentiated products, and free entry/exit. In the short run, firms behave like monopolies, earning profits or losses. In the long run, entry and exit shift demand curves until each firm's demand is tangent to its ATC, resulting in zero economic profit. Price exceeds MC, creating DWL, and firms do not produce at minimum ATC, leading to excess capacity.
垄断竞争市场中企业众多，产品有差异，且自由进出。短期中，企业像垄断者一样行动，获得利润或亏损。长期中，进出导致需求曲线移动，直至每个企业的需求曲线与ATC相切，经济利润为零。价格高于边际成本，造成无谓损失，且企业不在最低ATC生产，导致产能过剩。
Oligopoly is a market dominated by a few large firms, with interdependent decision-making. Key models include: kinked demand curve (price rigidity), Cournot (quantity competition), and game theory (prisoner’s dilemma). In a duopoly, outcome depends on whether firms collude (acting like a monopoly) or compete. Nash equilibrium occurs where each firm's strategy is optimal given the other's strategy. Collusion often leads to higher prices and restricted output.
寡头市场由少数几家大企业主导，决策相互依赖。主要模型包括：弯折的需求曲线（价格刚性）、古诺模型（数量竞争）和博弈论（囚徒困境）。在双头模型中，结果取决于企业是合谋（像垄断者一样行动）还是竞争。纳什均衡是在给定对方策略下每个企业的最优策略状态。合谋通常导致更高价格和受限产量。
Example: Two firms, A and B, decide to advertise or not. Payoff matrix (A's profit, B's profit): if both advertise (10, 10); if A advertises and B does not (20, 5); if B advertises and A does not (5, 20); if neither advertises (15, 15). Dominant strategy? For A, advertising yields 10 vs 5 if B advertises, 20 vs 15 if B doesn’t — always better. Same for B. Nash equilibrium is both advertise (10,10), though both would be better with no advertising (15,15). This is the prisoner’s dilemma.
例题：两家企业A和B，决定是否做广告。收益矩阵（A的利润，B的利润）：都做广告(10,10)；A做B不做(20,5)；B做A不做(5,20)；都不做(15,15)。占优策略？对于A，不论B是否做广告，A做广告总是更好（10 vs 5，20 vs 15）。B同理。纳什均衡为都做广告(10,10)，尽管都不做广告(15,15)对双方更好。这就是囚徒困境。
9. Factor Markets | 要素市场
uct demand. In a perfectly competitive labor market, firms hire workers where marginal revenue product (MRP) equals wage (W). MRP = marginal product of labor (MPL) × marginal revenue (MR). For a competitive product market, MR = P, so MRP = MPL × P (value of marginal product, VMP). Profit-maximizing employment is where MRP = wage. The supply of labor is upward-sloping, so the market wage is determined by intersection of labor demand and supply.
企业需求生产要素（劳动力、资本、土地）是因为它们有助于生产商品。要素需求是从产品需求派生的。在完全竞争的劳动力市场，企业在边际收益产品（MRP）等于工资（W）处雇佣工人。MRP = 劳动的边际产量（MPL） × 边际收益（MR）。对于竞争性产品市场，MR = P，所以 MRP = MPL × P（边际产品价值，VMP）。利润最大化就业点为 MRP = 工资。劳动供给曲线向上倾斜，市场工资由劳动需求和供给的交点决定。
e MFC = MRP and pays the wage from the supply curve at that quantity, resulting in lower employment and wage than competitive outcome. Unions can act as monopoly sellers of labor, attempting to raise wages above equilibrium.
如果企业是买方垄断（劳动力的单一买家），它面临向上倾斜的劳动供给曲线，因此边际要素成本（MFC）> 工资。它在 MFC = MRP 处雇佣，并按该数量从供给曲线上确定工资，导致就业和工资低于竞争性结果。工会可以充当劳动力的垄断卖家，试图将工资提高到均衡之上。
Example: A perfectly competitive firm sells output at $ h adds 10. MRP = MPL × P. Worker 1 MRP = 200, 2 = 180, 3 = 150, 4 = 100. If market wage is $160, the firm hires 3 workers because the 4th's MRP (100) < wage. Total product = 20+18+15 = 53 units.
例题：某完全竞争企业以每单位$10出售产品。其MPL表：第1个工人生产20单位，第2个增加18，第3个增加15，第4个增加10。MRP = MPL × P。工人1 MRP = 200，2 = 180，3 = 150，4 = 100。若市场工资为$160，企业雇佣3个工人，因为第4个的MRP(100) < 工资。总产量 = 20+18+15 = 53单位。
10. Market Failure and Externalities | 市场失灵与外部性
Market failure occurs when the free market fails to allocate resources efficiently. Externalities are costs or benefits that affect third parties not involved in the transaction. Negative production externalities (e.g., pollution) cause overproduction because firms ignore external costs. The socially optimal quantity is where marginal social cost (MSC) equals marginal social benefit (MSB). With negative externality, MSC > MPC (marginal private cost), leading to a deadweight loss from overproduction. Government can impose a Pigouvian tax equal to the external cost to internalize the externality.
当自由市场无法有效配置资源时，就发生市场失灵。外部性是指影响未参与交易的第三方的成本或收益。负生产外部性（如污染）会导致过度生产，因为企业忽视外部成本。社会最优产量位于边际社会成本（MSC）等于边际社会收益（MSB）处。存在负外部性时，MSC > MPC（边际私人成本），导致过度生产造成无谓损失。政府可征收等于外部成本的庇古税来内部化外部性。
Positive externalities (e.g., education, vaccines) lead to underproduction because private benefits are lower than social benefits. With positive consumption externalities, MSB > MPB, market quantity is too low. A Pigouvian subsidy can increase quantity to socially optimal level. Another type of market failure is public goods, which are non-rival and non-excludable, leading to the free-rider problem and underproduction by private markets.
正外部性（如教育、疫苗）会导致生产不足，因为私人收益低于社会收益。存在正消费外部性时，MSB > MPB，市场产量过低。庇古补贴可将产量提高至社会最优水平。另一种市场失灵是公共品，它们具有非竞争性和非排他性，导致搭便车问题和私人市场供给不足。
Example: A steel plant's private MC is 2Q, but it also emits pollution costing society $ of steel. Demand: P = 100 - Q. Private optimum: MR = MC, assuming perfect competition P=MC? + 10 → 100 - Q = 2Q + 10 → 90 = 3Q → Q = 30. Overproduction of 3.3 units. Pigouvian tax of $10 per unit shifts MPC to MSC, achieving Q=30.
例题：某钢厂的私人MC为2Q，但每生产1单位钢还产生污染，使社会承担$10成本。需求：P = 100 - Q。私人最优：在竞争市场，P = MPC：100 - Q = 2Q → Q ≈ 33.3。社会最优：P = MSC = 2Q + 10 → 100 - Q = 2Q + 10 → 90 = 3Q → Q = 30。过度生产约3.3单位。每单位$10的庇古税将使MPC上移至MSC，实现Q=30。
11. Public Goods and Common Resources | 公共品与公共资源
Goods can be classified by rivalry and excludability. Private goods are rival and excludable. Public goods are non-rival and non-excludable (e.g., national defense, lighthouses). Because people can benefit without paying, private markets undersupply public goods. The efficient quantity is where the sum of individual marginal benefits equals marginal cost (vertical summation of demand curves). Governments typically provide or subsidize public goods.
商品可按竞争性和排他性分类。私人物品具有竞争性和排他性。公共品具有非竞争性和非排他性（如国防、灯塔）。因为人们可以不付费就受益，私人市场对公共品的供给不足。有效数量是个人边际收益之和等于边际成本处（需求曲线的垂直加总）。政府通常提供或补贴公共品。
Common resources are rival but non-excludable (e.g., fisheries, clean air). They suffer from the "tragedy of the commons," where individuals overuse and deplete the resource. Solutions include regulation, tradable permits, or property rights assignment. Quasi-public goods (e.g., cable TV) are excludable but non-rival, and private markets can supply them.
公共资源具有竞争性但非排他性（如渔业、清洁空气）。它们面临“公地悲剧”，即个体过度使用并耗尽资源。解决办法包括管制、可交易许可证或产权界定。准公共品（如有线电视）具有排他性但非竞争性，可由私人市场供给。
r A’s demand: Pa = 50 - Q, B’s demand: Pb = 30 - Q. Marginal cost of patrol is constant at $ to MC. Without coordination, each would buy where private MB=MC (or share cost), leading to underprovision.
例题：两个邻居看重保安巡逻。A的需求：Pa = 50 - Q，B的需求：Pb = 30 - Q。巡逻的边际成本恒为每小时$60。作为公共品，社会MB = Pa + Pb = 80 - 2Q。最优Q：80 - 2Q = 60 → 2Q = 20
Published by TutorHao | AP Economics Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图