📚 Year 8 CIE Economics: Formula & Theorem Quick Reference Handbook | 公式定理速查手册
This handbook brings together the essential formulas, theorems and key definitions you need for Year 8 CIE Economics. It is designed as a quick revision tool to help you master the core principles — from scarcity and opportunity cost to market equilibrium and elasticity. Review each section regularly to build confidence and fluency in applying economic reasoning.
本手册汇集了 Year 8 CIE 经济学所需的基本公式、定理和关键定义。它是一份快速复习工具，旨在帮助你掌握从稀缺性和机会成本到市场均衡和弹性等核心原理。定期回顾每个部分，逐步建立信心并熟练运用经济推理。
1. The Economic Problem: Scarcity & Choice | 经济问题：稀缺性与选择
The fundamental economic problem is scarcity: finite resources cannot satisfy infinite human wants. Because land, labour, capital and enterprise are limited, every society must answer three questions — what to produce, how to produce and for whom to produce. Choice is inevitable, and every choice carries a cost.
基本经济问题是稀缺性：有限的资源无法满足无止境的人类欲望。由于土地、劳动力、资本和企业才能都是有限的，每个社会都必须回答三个问题——生产什么、如何生产以及为谁生产。选择不可避免，且每一个选择都伴随着成本。
2. Opportunity Cost Formula | 机会成本公式
Opportunity Cost = Value of Next Best Alternative Forgone
Opportunity cost is the highest-valued alternative sacrificed when a decision is made. It is not the total of all foregone options, but only the single most desirable one. When a government spends on defence instead of health, the opportunity cost is the forgone benefit from better hospitals, not the sum of all other public services.
机会成本是做出决策时所放弃的最高价值替代品。它不是所有被放弃选项的总和，而仅仅是其中最具吸引力的那一个。当政府将资金用于国防而非医疗时，机会成本是所放弃的更好医院带来的好处，而非所有其他公共服务的总和。
3. Factors of Production | 生产要素
Land includes all natural resources such as minerals, forests and water. Labour is human physical and mental effort. Capital consists of man-made tools, machinery and buildings used to produce other goods. Enterprise is the ability to organise the other three factors and bear business risks. The rewards are rent, wages, interest and profit.
土地包括矿产、森林和水等自然资源。劳动是人的体力和脑力付出。资本由用于生产其他商品的人造工具、机器和建筑物组成。企业才能则指组织其他三种要素并承担商业风险的能力。其报酬依次为租金、工资、利息和利润。
4. Demand and the Law of Demand | 需求与需求定律
Demand reflects both willingness and ability to buy. The law of demand holds that, ceteris paribus, a rise in price leads to a fall in quantity demanded. The demand curve slopes downward. A simple linear demand function is:
需求反映了购买意愿和购买能力。需求定律指出，其他条件不变时，价格上升导致需求量下降。需求曲线向下倾斜。一个简单的线性需求函数为：
Qd = a − bP
where Qd is quantity demanded, P is price, a is the quantity that would be demanded if price were zero, and b measures the responsiveness of demand to price changes. A shift in demand occurs when factors such as income, tastes or the price of related goods change.
其中 Qd 为需求量，P 为价格，a 为价格为零时的需求量，b 衡量需求量对价格变动的反应程度。当收入、偏好或相关商品价格等因素变化时，需求曲线发生位移。
5. Supply and the Law of Supply | 供给与供给定律
Supply is the amount producers are ready to sell at given prices. The law of supply states that, ceteris paribus, quantity supplied rises as price rises. The supply curve slopes upward. A typical linear supply function is:
供给是生产者在给定价格下愿意出售的数量。供给定律指出，其他条件不变时，价格上升，供给量增加。供给曲线向上倾斜。典型的线性供给函数为：
Qs = c + dP
where Qs is quantity supplied, c is the minimum amount supplied (often zero or negative), and d captures how strongly supply reacts to price. Shifts arise from cost changes, technology, taxes or subsidies.
其中 Qs 为供给量，c 为最低供给量（通常为零或负数），d 体现供给对价格的反应强度。成本变化、技术、税收或补贴会引起供给曲线位移。
6. Market Equilibrium: Price Mechanism | 市场均衡：价格机制
Equilibrium occurs where quantity demanded equals quantity supplied. At this point, plans of buyers and sellers match, and there is no tendency for price to change. The condition is:
均衡发生在需求量等于供给量之时。此刻买卖双方的计划相互匹配，价格没有变动的趋势。均衡条件为：
Qd = Qs
ear demand and supply: a − bP = c + dP. Solving yields the equilibrium price and quantity:
利用线性需求和供给：a − bP = c + dP，可解得均衡价格和数量：
P* = (a − c) / (b + d)
Q* = a − bP* = c + dP*
The price mechanism rations scarce goods to those willing and able to pay, signals producers about where resources are needed, and incentivises efficient production.
价格机制把稀缺商品分配给愿意并有能力支付的人，向生产者发出资源需求的信号，并激励高效生产。
7. Price Elasticity of Demand (PED) | 需求的价格弹性
PED measures how sensitive quantity demanded is to a price change. The basic formula using percentages is:
PED 衡量需求量对价格变动的敏感程度。基于百分比的基本公式为：
PED = %ΔQd / %ΔP
and is less responsive. Unit elasticity (PED = 1) means total revenue stays constant when price changes.
若 PED > 1（富有弹性），需求反应剧烈；降价使需求量增长幅度大于价格下降幅度。若 PED < 1（缺乏弹性），需求反应微弱。单位弹性（PED = 1）意味着价格变动时总收益保持不变。
8. Total Revenue and PED | 总收益与需求价格弹性
Total Revenue (TR) = Price × Quantity Sold
The link between PED and total revenue is a vital theorem. When demand is elastic, lowering price increases total revenue because the percentage rise in quantity outweighs the percentage fall in price. Conversely, when demand is inelastic, raising price raises total revenue. If demand is unit elastic, total revenue stays the same.
PED 与总收益之间的联系是一项重要定理。当需求富有弹性时，降价增加总收益，因为需求量的百分比增长超过了价格的百分比下跌。反之，需求缺乏弹性时，提价增加总收益。如果需求为单位弹性，总收益不变。
9. Price Elasticity of Supply (PES) | 供给价格弹性
PES quantifies how quantity supplied reacts to price adjustments. The formula parallels that of PED:
PES 量化供给量对价格调整的反应。其公式与 PED 相似：
PES = %ΔQs / %ΔP
y, where producers can easily increase output. A PES less than 1 reflects inelastic supply — as a vertical supply curve, while perfectly elastic supply (PES = ∞) has a horizontal one.
PES 大于 1 表示供给富有弹性，生产者能轻松增加产出。PES 小于 1 表示供给缺乏弹性——生产无法快速扩大。完全无弹性供给（PES = 0）的供给曲线是垂直的，而完全弹性供给（PES = ∞）的供给曲线是水平的。
10. Consumer and Producer Surplus | 消费者剩余与生产者剩余
Consumer surplus is the benefit buyers get from paying less than their maximum willingness to pay. Producer surplus is the benefit sellers get from receiving more than their minimum acceptable price. In diagrammatic terms:
消费者剩余是消费者因实际支付低于最高支付意愿而获得的福利。生产者剩余是生产者因收到的价格高于最低可接受价格而获得的福利。用公式表示为：
Consumer Surplus = Total Willingness to Pay − Total Actual Payment
Producer Surplus = Total Revenue − Total Variable Cost
In a competitive market, total surplus (consumer plus producer) is maximised at equilibrium, indicating allocative efficiency.
在竞争市场中，总剩余（消费者剩余加生产者剩余）在均衡状态达到最大，体现配置效率。
11. The Functions of Money | 货币的功能
Money performs four key functions in a modern economy: medium of exchange (it removes the need for a double coincidence of wants), unit of account (prices are expressed in a common measure), store of value (it preserves purchasing power over time), and standard of deferred payment (it enables borrowing and lending).
货币在现代经济中执行四项核心功能：交换媒介（消除需求的双重巧合），记账单位（价格用统一尺度表示），价值储藏（长期保有购买力）以及延期支付标准（使借贷成为可能）。
12. Inflation Rate Calculation | 通货膨胀率计算
Inflation measures the sustained rise in the general price level. The Consumer Price Index (CPI) is commonly used. The simple inflation rate between two periods is:
通货膨胀衡量总体价格水平的持续上升。通常使用消费者价格指数（CPI）。两个时期之间的简单通货膨胀率为：
Inflation Rate = (CPI New − CPI Old) / CPI Old × 100%
where CPI Old is the index for the earlier period and CPI New is the index for the later period. A positive value signals inflation; a negative value indicates deflation. Central banks use this formula to guide monetary policy.
其中 CPI Old 代表较早时期的指数，CPI New 代表较晚时期的指数。正值表示通货膨胀，负值表示通货紧缩。中央银行以此公式指导货币政策。
Published by TutorHao | Economics Revision Series | aleveler.com
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