Formula and Theorem Quick Reference Handbook for Year 13 Cambridge Economics | A2经济公式定理速查手册

📚 Formula and Theorem Quick Reference Handbook for Year 13 Cambridge Economics | A2经济公式定理速查手册

This handbook provides a concise reference to the essential formulas, theorems, and key concepts required for Year 13 Cambridge Economics. It covers both microeconomic and macroeconomic topics, helping you to quickly recall and apply critical relationships in your analysis and exam answers.

本手册为 Year 13 剑桥 A-Level 经济学考试提供核心公式、定理及关键概念的速查。涵盖微观与宏观两大领域，帮助你快速回顾并准确运用重要关系进行分析与答题。

1. Elasticities | 弹性

Price Elasticity of Demand (PED) = %ΔQd / %ΔP — measures responsiveness of quantity demanded to price changes. Midpoint formula: PED = (ΔQ / [(Q₁+Q₂)/2]) / (ΔP / [(P₁+P₂)/2]).

需求价格弹性 (PED) = %ΔQd / %ΔP — 衡量需求量对价格变动的反应程度。中点公式：PED = (ΔQ / [(Q₁+Q₂)/2]) / (ΔP / [(P₁+P₂)/2])。

If |PED| > 1, demand is price elastic. If |PED| < 1, demand is price inelastic. If |PED| = 1, demand is unit elastic.

若 |PED| > 1，需求富有价格弹性；若 |PED| < 1，需求缺乏价格弹性；若 |PED| = 1，需求为单位弹性。

Income Elasticity of Demand (YED) = %ΔQd / %ΔY. YED > 0 for normal goods; YED < 0 for inferior goods. Luxury goods have YED > 1, necessities have 0 < YED < 1.

需求的收入弹性 (YED) = %ΔQd / %ΔY。正常品的 YED > 0；低档品的 YED < 0。奢侈品 YED > 1，必需品 0 < YED < 1。

Cross Elasticity of Demand (XED) = %ΔQd of Good A / %ΔP of Good B. Substitutes have XED > 0; complements have XED < 0.

需求的交叉弹性 (XED) = 商品A需求量的%变化 / 商品B价格的%变化。替代品的 XED > 0；互补品的 XED < 0。

Price Elasticity of Supply (PES) = %ΔQs / %ΔP. Determinants include time period, spare capacity, and stock levels.

供给价格弹性 (PES) = %ΔQs / %ΔP。影响因素包括时间长短、闲置产能及存货水平。

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2. Costs, Revenue and Profit Maximisation | 成本、收益与利润最大化

Total Cost (TC) = Total Fixed Cost (TFC) + Total Variable Cost (TVC). Average Cost (AC) = TC / Q. Marginal Cost (MC) = ΔTC / ΔQ.

总成本 (TC) = 总固定成本 (TFC) + 总可变成本 (TVC)。平均成本 (AC) = TC / Q。边际成本 (MC) = ΔTC / ΔQ。

Total Revenue (TR) = Price × Quantity. Average Revenue (AR) = TR / Q = P. Marginal Revenue (MR) = ΔTR / ΔQ.

总收益 (TR) = 价格 × 数量。平均收益 (AR) = TR / Q = P。边际收益 (MR) = ΔTR / ΔQ。

Profit maximisation occurs where MR = MC. This is the first-order condition; the firm must also ensure MC cuts MR from below.

利润最大化发生在 MR = MC 处。这是一阶条件；企业还需确保 MC 自下而上穿过 MR。

Short-run shutdown condition: if P < AVC, the firm minimises losses by shutting down.

短期停产条件：若 P < AVC，企业通过停产使亏损最小化。

Normal profit occurs when AR = AC. Supernormal profit when AR > AC.

正常利润发生在 AR = AC 时。超常利润出现在 AR > AC。

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3. Market Structures and Efficiency | 市场结构与效率

In perfect competition, the firm is a price-taker: P = MR = AR = D. Long-run equilibrium: P = MC = min AC, achieving both allocative and productive efficiency.

在完全竞争中，企业为价格接受者：P = MR = AR = D。长期均衡：P = MC = 最低 AC，同时实现配置效率与生产效率。

Allocative efficiency: P = MC. Productive efficiency: P = minimum AC.

配置效率：P = MC。生产效率：P = 最低 AC。

Monopoly profit maximisation: MR = MC, but price is found on the demand curve, so P > MC, creating a deadweight loss.

垄断利润最大化：MR = MC，但价格由需求曲线决定，故 P > MC，产生无谓损失。

Price discrimination: a monopolist charges different prices for different consumers. Conditions: market power, ability to prevent resale, and different price elasticities of demand.

价格歧视：垄断者对不同消费者收取不同价格。条件：具有市场势力、能防止转售、且不同消费者群体的需求价格弹性不同。

In oligopoly, the kinked demand curve explains price rigidity: MR is discontinuous, so MC can shift within a range without changing the profit-maximising price.

在寡头垄断中，折弯的需求曲线解释了价格刚性：MR 不连续，因此 MC 在一定范围内变动也不会改变利润最大化价格。

Game theory: Nash equilibrium occurs when each player chooses the best strategy given the strategies of others. Prisoner’s Dilemma shows a conflict between individual and collective rationality.

博弈论：纳什均衡发生在一方给定对方策略时选择自身最优策略的情况下。囚徒困境显示出个体理性与集体理性之间的冲突。

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4. Labour Market and Wage Determination | 劳动力市场与工资决定

Demand for labour: The Marginal Revenue Product of Labour MRP_L = MPP × MR. Under perfect competition in the product market, MR = P, so MRP_L = MPP × P.

劳动力需求：劳动的边际收益产品 MRPₗ = MPP × MR。若产品市场为完全竞争，MR = P，因此 MRPₗ = MPP × P。

The firm hires labour up to the point where MRP_L = wage (w).

企业雇用劳动直至 MRPₗ = 工资 (w) 这一点。

Monopsony: a single buyer of labour. The Marginal Cost of Labour (MCL) lies above the supply curve of labour, so the profit-maximising level of employment is where MCL = MRP_L, resulting in lower employment and a lower wage than a competitive labour market.

买方垄断：劳动的单一买家。劳动的边际成本 (MCL) 位于劳动供给曲线之上，因此利润最大化的雇用水平由 MCL = MRPₗ 决定，导致就业量与工资均低于竞争性劳动市场。

Trade unions can shift the supply of labour, negotiate higher wages, and potentially create a wage differential above equilibrium.

工会可以移动劳动供给、谈判提高工资，并可能在均衡水平之上产生工资差异。

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5. Market Failure and Government Intervention | 市场失灵与政府干预

Social cost = Private cost + External cost. Social benefit = Private benefit + External benefit. Market failure occurs when the free market does not achieve social efficiency.

社会成本 = 私人成本 + 外部成本。社会收益 = 私人收益 + 外部收益。当自由市场未能实现社会效率时，便出现市场失灵。

Negative production externality: over-production because Social Cost > Private Cost. A Pigouvian tax can be set equal to the marginal external cost at the socially optimal output (Q_social).

负生产外部性：因 社会成本 > 私人成本 而导致过度生产。庇古税可设定为等于社会最优产量 (Q_social) 处的边际外部成本。

Positive consumption externality: under-consumption because Social Benefit > Private Benefit. A subsidy equal to the marginal external benefit at Q_social can internalise the externality.

正消费外部性

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