📚 AP Microeconomics Knowledge Points Systematic Review | AP微观经济学知识点系统梳理
This article provides a comprehensive review of the core concepts tested in AP Microeconomics, organized into ten key sections. Mastering these topics is essential for exam success and for understanding how individuals and firms make decisions under scarcity.
本文系统梳理了AP微观经济学考试涉及的十大核心知识点模块，覆盖从基础经济概念到市场失灵的全范围。掌握这些内容是取得高分的关键，也有助于理解个人和企业在稀缺性下的决策逻辑。
1. Basic Economic Concepts | 基本经济概念
Scarcity forces individuals, firms, and societies to make choices because resources are limited relative to unlimited wants.
稀缺性迫使个人、企业和社会做出选择，因为相对于无限欲望，资源是有限的。
The opportunity cost of any choice is the value of the next best alternative foregone.
任何选择的机会成本是所放弃的次优方案的价值。
Rational decision-makers compare marginal benefits and marginal costs; an action should be taken if MB ≥ MC.
理性决策者会比较边际收益和边际成本；当边际收益大于等于边际成本时应采取该行动。
The production possibilities curve (PPC) illustrates trade-offs, efficiency, and economic growth. Points inside the curve indicate inefficiency, while outward shifts represent growth in productive capacity.
生产可能性曲线（PPC）展示了权衡取舍、效率与经济增长。曲线内的点表示无效率，向外移动代表生产能力的增长。
Comparative advantage—the ability to produce a good at a lower opportunity cost—drives specialization and mutually beneficial trade.
比较优势——以更低的机会成本生产某种商品的能力——推动了专业化与互利贸易。
2. Supply and Demand | 供给与需求
The law of demand states that, ceteris paribus, as price rises, quantity demanded falls. The demand curve slopes downward.
需求定律指出，在其他条件不变时，价格上升，需求量下降。需求曲线向下倾斜。
The law of supply states that, ceteris paribus, as price rises, quantity supplied increases. The supply curve slopes upward.
供给定律指出，在其他条件不变时，价格上升，供给量增加。供给曲线向上倾斜。
The intersection of supply and demand curves determines equilibrium price (P*) and equilibrium quantity (Q*).
供给曲线与需求曲线的交点决定了均衡价格(P*)和均衡数量(Q*)。
Changes in non-price determinants (e.g., income, tastes, input costs, technology) shift the curves, while changes in price cause movements along the curves.
非价格决定因素（如收入、偏好、投入成本、技术）的变化导致曲线移动，而价格变化则引起沿曲线的移动。
3. Elasticity | 弹性
Price elasticity of demand (PED) measures responsiveness of quantity demanded to a price change: PED = %ΔQd / %ΔP. If |PED| > 1, demand is elastic; if |PED| < 1, inelastic; if |PED| = 1, unit elastic.
需求价格弹性（PED）衡量需求量对价格变化的反应程度：PED = %ΔQd / %ΔP。若 |PED| > 1，需求富有弹性；|PED| < 1，缺乏弹性；|PED| = 1，单位弹性。
Use the midpoint formula: %Δ = (New – Old) / [(New + Old)/2] × 100 to avoid inconsistency in calculating percentage changes.
使用中点公式：变化百分比 = (新值 – 旧值) / [(新值 + 旧值)/2] × 100，以避免计算变化百分比时的不一致。
Determinants of PED include availability of substitutes, necessity vs. luxury, time horizon, and proportion of income spent on the good.
需求弹性的影响因素包括替代品的可得性、必需品与奢侈品、时间范围以及该商品在消费者支出中的占比。
Total revenue test: if demand is elastic, a price increase reduces total revenue (TR = P × Q); if inelastic, total revenue rises with price.
总收入检验：若需求富有弹性，提价会减少总收入(TR = P × Q)；若缺乏弹性，总收入随价格上升而增加。
Cross-price elasticity of demand: Exy = %ΔQd of good X / %ΔP of good Y; positive for substitutes, negative for complements.
需求交叉弹性：Exy = 商品X需求量变化百分比 / 商品Y价格变化百分比；替代品为正，互补品为负。
Income elasticity: Ey = %ΔQd / %ΔIncome; positive for normal goods, negative for inferior goods.
收入弹性：Ey = %ΔQd / %Δ收入；正常品为正，劣等品为负。
Price elasticity of supply measures how quickly producers can adjust output; it depends on time and flexibility of production.
供给价格弹性衡量生产者调整产出的速度；取决于时间和生产的灵活性。
4. Consumer Choice Theory | 消费者选择理论
Utility is the satisfaction derived from consumption; total utility increases as more is consumed, but marginal utility declines (law of diminishing marginal utility).
效用是消费带来的满足感；消费量增加时总效用增加，但边际效用递减（边际效用递减规律）。
Consumers maximize utility when the marginal utility per dollar spent is equal across all goods: MUa/Pa = MUb/Pb = … subject to budget constraint.
消费者在每一种商品上花费的最后一美元的边际效用相等时实现效用最大化：MUa/Pa = MUb/Pb = …，并受预算约束。
When the price of a good falls, the substitution effect leads the consumer to buy more of that good because it is relatively cheaper; the income effect may further increase or decrease consumption depending on whether the good is normal or inferior.
当某种商品价格下降时，替代效应使得消费者购买更多该商品，因为它相对更便宜；收入效应可能进一步增加或减少消费，取决于该商品是正常品还是劣等品。
5. Production and Costs | 生产与成本
In the short run, at least one input is fixed; the law of diminishing marginal returns says that as more of a variable input is added to fixed inputs, marginal product eventually decreases.
在短期，至少一种投入是固定的；边际报酬递减规律指出，当在固定投入上增加更多可变投入时，边际产量最终会下降。
Total cost (TC) = total fixed cost (TFC) + total variable cost (TVC). ATC = TC/Q, AVC = TVC/Q, AFC = TFC/Q, and MC = ΔTC/ΔQ.
总成本(TC) = 总固定成本(TFC) + 总可变成本(TVC)。平均总成本(ATC) = TC/Q，平均可变成本(AVC) = TVC/Q，平均固定成本(AFC) = TFC/Q，边际成本(MC) = ΔTC/ΔQ。
MC cuts ATC and AVC at their minimum points. The ATC curve is U-shaped due to spreading fixed costs and then diminishing returns.
MC曲线穿过ATC和AVC的最低点。ATC曲线呈U型，先是固定成本分摊效应，然后由于边际报酬递减而上升。
In the long run, all inputs are variable; firms experience economies of scale (decreasing LRATC), constant returns, or diseconomies of scale (increasing LRATC).
在长期，所有投入均可变；企业可能经历规模经济（长期平均总成本下降）、规模收益不变或规模不经济（长期平均总成本上升）。
6. Perfect Competition | 完全竞争
A perfectly competitive market has many small firms, identical products, perfect information, and free entry and exit. Firms are price takers; the individual firm’s demand curve is perfectly elastic at the market price.
完全竞争市场有大量小企业、同质产品、完全信息以及自由进入和退出。企业是价格接受者；单个企业面临的需求曲线在市场价格处完全有弹性。
Profit maximization occurs where MR = MC. Since P = MR, the rule becomes P = MC.
利润最大化发生在MR = MC处。由于P = MR，规则变为P = MC。
In the short run, a firm can earn economic profits or incur losses. If P < AVC, the firm should shut down to minimize losses.
在短期，企业可能获得经济利润或遭受亏损。若P < AVC，企业应停产以最小化损失。
In the long run, economic profits attract entry, shifting supply right and lowering price until P = ATC, and all firms earn normal profit (zero economic profit). Long-run equilibrium yields productive efficiency (P = minimum ATC) and allocative efficiency (P = MC).
在长期，经济利润吸引新企业进入，供给曲线右移，价格下降，直到P = ATC，所有企业赚取正常利润（
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