📚 Year 12 Cambridge Economics: Formula and Key Concepts Quick Reference Handbook | Year 12 剑桥经济：公式定理速查手册
This quick reference handbook brings together the essential formulas, key concepts and relationships that every Year 12 Cambridge Economics student must master. Covering both micro and macroeconomics, the guide is designed for rapid revision and easy memorisation. Each section presents the core equation or principle first in English, followed immediately by its Chinese equivalent, ensuring that bilingual learners can internalise the material in both languages.
本速查手册汇集了每一位Year 12剑桥经济学生必须掌握的核心公式、关键概念与数量关系。内容覆盖微观与宏观两大板块，专为快速复习和高效记忆而设计。每一节先用英文呈现核心公式或定理，紧接中文对应表述，帮助双语学习者在两种语言中同步内化所学内容。
1. Price Elasticity of Demand (PED) | 需求价格弹性
The responsiveness of quantity demanded to a change in price is captured by the price elasticity of demand. A value greater than 1 in absolute terms signals elastic demand, while a value less than 1 indicates inelastic demand.
需求量对价格变动的反应程度由需求价格弹性衡量。绝对值大于1表示需求富有弹性，小于1则表示需求缺乏弹性。
PED = %ΔQd / %ΔP
Key interpretations:
- |PED| > 1: elastic – revenue rises when price falls.
- |PED| < 1: inelastic – revenue falls when price falls.
- |PED| = 1: unit elastic – revenue is maximised.
- PED = 0: perfectly inelastic; PED = ∞: perfectly elastic.
关键解读：
- |PED| > 1：富有弹性 —— 降价使总收入增加。
- |PED| < 1：缺乏弹性 —— 降价使总收入减少。
- |PED| = 1：单位弹性 —— 总收入达到最大。
- PED = 0：完全无弹性；PED = ∞：完全弹性。
2. Income Elasticity of Demand (YED) | 需求收入弹性
Income elasticity of demand measures how quantity demanded responds to changes in consumer income. The sign and magnitude classify goods as normal, luxury, or inferior.
需求收入弹性衡量需求量对消费者收入变化的敏感程度，其正负号及数值大小可用于区分正常品、奢侈品和低档品。
YED = %ΔQd / %ΔY
Classification:
- YED > 0: normal good. If YED > 1, it is a luxury; if 0 < YED < 1, it is a necessity.
- YED < 0: inferior good – demand falls as income rises.
分类：
- YED > 0：正常品。若YED > 1则为奢侈品；若 0 < YED < 1则为必需品。
- YED < 0：低档品 —— 收入上升时需求反而下降。
3. Cross Elasticity of Demand (XED) | 需求交叉弹性
Cross elasticity of demand shows the relationship between the price of one good and the quantity demanded of another. It helps identify substitutes and complements.
需求交叉弹性反映一种商品价格变化对另一种商品需求量的影响，据此可判断替代品与互补品关系。
XED = %ΔQd of good A / %ΔP of good B
Interpretation:
- XED > 0: substitutes (e.g. tea and coffee).
- XED < 0: complements (e.g. printers and ink).
- XED ≈ 0: independent goods.
解读：
- XED > 0：替代品（如茶与咖啡）。
- XED < 0：互补品（如打印机与墨盒）。
- XED ≈ 0：独立品。
4. Price Elasticity of Supply (PES) | 供给价格弹性
Price elasticity of supply measures the responsiveness of quantity supplied to a change in price. It depends largely on production flexibility and time.
供给价格弹性衡量供给量对价格变动的反应程度，其主要取决于生产灵活性与时间周期。
PES = %ΔQs / %ΔP
Key points:
- PES > 1: elastic supply – producers can quickly increase output.
- PES < 1: inelastic supply – output is constrained in the short run.
- PES = 0: perfectly inelastic (fixed supply); PES = ∞: perfectly elastic.
要点：
- PES > 1：弹性供给 —— 生产者能快速扩大产出。
- PES < 1：缺乏弹性 —— 短期产出受限。
- PES = 0：完全无弹性（供给固定）；PES = ∞：完全弹性。
5. Utility and Consumer Choice | 效用与消费者选择
Consumers aim to maximise total utility given their budget. The law of diminishing marginal utility states that as consumption of a good increases, the additional satisfaction from each extra unit eventually falls.
消费者在既定预算下追求总效用最大化。边际效用递减规律表明，随着对某种商品消费量的增加，每额外一单位所带来的满足感最终会下降。
MU = ΔTU / ΔQ
Equi‑marginal principle (utility maximisation condition):
MUx / Px = MUy / Py
The consumer allocates spending so that the last pound spent on each good yields the same marginal utility.
等边际原理（效用最大化条件）：
消费者将支出分配至各商品的最后一英镑所带来的边际效用相等。
6. Costs of Production | 生产成本
A firm incurs fixed and variable costs. Understanding these cost relationships is essential for analysing firm behaviour.
企业承担固定成本与可变成本。理解这些成本关系是分析企业行为的基础。
TC = TFC + TVC
AFC = TFC / Q
AVC = TVC / Q
AC = TC / Q = AFC + AVC
MC = ΔTC / ΔQ
Short‑run cost relationships: the marginal cost curve intersects both AVC and AC at their minimum points.
短期成本关系：边际成本曲线与平均可变成本曲线、平均成本曲线分别相交于后两者最低点。
7. Revenues and Profit Maximisation | 收益与利润最大化
Revenue concepts are the other side of the profit equation. The profit‑maximising rule holds for all market structures.
收益概念是利润方程的另一面。利润最大化规则适用于所有市场结构。
TR = P × Q
AR = TR / Q = P
MR = ΔTR / ΔQ
Profit maximisation: MC = MR
When marginal cost equals marginal revenue, profit is maximised (or losses minimised). If MR > MC, the firm can increase profit by producing more; if MR < MC, it should reduce output.
当边际成本等于边际收益时，利润达到最大（或亏损最小）。若MR > MC，增产可增加利润；若MR < MC，则减产才能避免利润下滑。
8. Market Structures Overview | 市场结构概述
Market structures differ by number of firms, barriers to entry, product differentiation, and the firm’s price‑setting power. The table below summarises key characteristics.
市场结构因厂商数量、进入壁垒、产品差异化程度以及企业定价能力而不同。下表汇总了关键特征。
| Feature / 特征 | Perfect Competition / 完全竞争 | Monopolistic Competition / 垄断竞争 | Oligopoly / 寡头垄断 | Monopoly / 完全垄断 |
|---|---|---|---|---|
| Number of firms / 厂商数量 | Many | Many | Few large firms | One |
| Barriers to entry / 进入壁垒 | None | Low | High | Very high / blocked |
| Product type / 产品类型 | Homogeneous | Differentiated | Can be homogeneous or differentiated | Unique, no close substitutes |
| Price setting power / 定价能力 | Price taker (P = MR = AR) | Some price‑setting ability | Interdependent pricing | Price maker |
| Efficiency in long run / 长期效率 | Allocatively and productively efficient | Neither in long‑run equilibrium | Often socially inefficient | Inefficient unless regulated |
In perfect competition, short‑run abnormal profits attract new entrants, driving price down until normal profits are made. Monopolies can sustain abnormal profits in the long run because of high barriers.
在完全竞争中，短期超额利润吸引新厂商进入，直至价格降至正常利润水平。垄断企业则因高壁垒得以长期维持超额利润。
9. Macroeconomic Indicators | 宏观经济指标
Key macroeconomic performance metrics include GDP, inflation, and unemployment. Understanding their calculation is fundamental for policy analysis.
关键的宏观经济表现指标包括国内生产总值、通货膨胀率和失业率。理解其计算方法是政策分析的基础。
GDP Deflator = (Nominal GDP / Real GDP) × 100
Inflation Rate = (CPIcurrent − CPIprevious) / CPIprevious × 100%
Unemployment Rate = (Number of unemployed / Labour force) × 100%
Other vital identities:
- Labour force = employed + unemployed (actively seeking work).
- Economic growth rate = (ΔReal GDP / Original Real GDP) × 100%.
- GDP per capita = Real GDP / Population.
其他重要恒等式：
- 劳动力 = 就业人数 + 失业人数（正在积极求职者）。
- 经济增长率 = (Δ实际GDP / 原实际GDP) × 100%。
- 人均GDP = 实际GDP / 人口。
10. The Multiplier Effect | 乘数效应
The multiplier quantifies the magnified impact of an initial injection into the circular flow on the final level of national income. It depends on the marginal propensities to consume and save.
乘数量化了初始注入资金对国民收入最终水平的放大效应，其大小取决于边际消费倾向与边际储蓄倾向。
Multiplier (k) = 1 / (1 − MPC) = 1 / MPS
where MPC + MPS = 1. The larger the MPC, the larger the multiplier. The process operates because one person’s spending becomes another’s income, generating successive rounds of expenditure.
其中MPC + MPS = 1。边际消费倾向越高，乘数越大。乘数过程得以运行，是因为一方的支出成为另一方的收入，进而引发一轮又一轮的消费。
Application: An initial increase in government spending or investment (ΔJ) raises national income by k × ΔJ. The effect is dampened by leakages such as taxes, saving, and imports.
应用：初始政府支出或投资增加（ΔJ）将使国民收入上升k × ΔJ。税收、储蓄和进口等漏出因素会削弱乘数效果。
Published by TutorHao | Economics Revision Series | aleveler.com
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