📚 Year 9 WJEC Economics: Formula & Theorem Quick Reference Handbook | Year 9 WJEC 经济：公式定理速查手册
This handbook provides a concise yet comprehensive overview of the essential formulas, definitions and economic theorems required for the Year 9 WJEC Economics syllabus. It is designed as a revision tool to help students quickly recall key concepts, from basic economic ideas to applied calculations. Mastering these fundamentals will build a solid foundation for GCSE Economics and beyond.
本手册简明而全面地概述了 Year 9 WJEC 经济学教学大纲所要求的基本公式、定义和经济定理。它被设计为一种复习工具，帮助学生快速回忆从基本经济概念到应用计算的关键知识点。掌握这些基础知识将为 GCSE 经济学及更深层次的学习打下坚实基础。
1. Scarcity, Choice and Opportunity Cost | 稀缺性、选择与机会成本
The fundamental economic problem states that resources are finite while human wants are infinite. This condition of scarcity forces individuals, firms and governments to make choices. Every choice involves a trade-off, meaning that selecting one option requires giving up the next best alternative.
基本经济问题指出，资源是有限的，而人类的欲望是无限的。这种稀缺性迫使个人、企业和政府做出选择。每一个选择都涉及权衡取舍，意味着选择一个选项就必须放弃次优替代方案。
The opportunity cost is defined as the value of the next best alternative forgone when a decision is made. It is not simply the sum of all alternatives given up, but specifically the single most desirable option sacrificed. For a student deciding to study instead of working part-time, the opportunity cost is the wage income lost, not the lost leisure time.
机会成本被定义为做出决策时所放弃的次优替代方案的价值。它不仅仅是被放弃的所有替代方案的总和，而是特指牺牲掉的唯一最渴望的选项。对于一个决定学习而非做兼职的学生来说，机会成本是损失的工资收入，而不是损失的休闲时间。
Opportunity Cost = Value of Next Best Alternative Forgone
机会成本 = 所放弃的次优替代方案的价值
2. Factors of Production and Their Rewards | 生产要素及其报酬
Resources used to produce goods and services are classified into four factors of production. Each factor receives a corresponding reward or income in the production process. Understanding these categories is essential for analysing how an economy organises its resource allocation.
用于生产商品和服务的资源被分为四种生产要素。每种要素在生产过程中都会获得相应的报酬或收入。理解这些分类对于分析经济体如何组织其资源配置至关重要。
| Factor of Production / 生产要素 | Definition / 定义 | Reward / 报酬 |
|---|---|---|
| Land / 土地 | Natural resources available for production. / 可用于生产的自然资源。 | Rent / 租金 |
| Labour / 劳动 | Human effort, both physical and mental, used in production. / 生产中使用的体力和脑力劳动。 | Wages/Salaries / 工资/薪水 |
| Capital / 资本 | Man-made goods used to produce other goods, e.g. machinery. / 用于生产其他商品的人造商品，如机器。 | Interest / 利息 |
| Enterprise / 企业家才能 | The willingness to take risks and combine the other three factors. / 承担风险并组合其他三种要素的意愿。 | Profit / 利润 |
3. The Production Possibility Frontier (PPF) | 生产可能性边界
A Production Possibility Frontier illustrates the maximum possible output combinations of two goods or services that an economy can achieve when all resources are fully and efficiently employed. Points on the curve represent productive efficiency, while points inside the curve indicate underutilisation of resources.
生产可能性边界展示了一个经济体在充分且有效利用所有资源时，能够实现的两种商品或服务的最大可能产出组合。曲线上的点代表生产效率，而曲线内的点则表示资源未被充分利用。
An outward shift of the PPF indicates economic growth, caused by an increase in the quantity or quality of factors of production. Technological advancement or an increase in the labour force are typical drivers. A point outside the PPF is currently unattainable given existing resources and technology. The bowed-out shape reflects the principle of increasing opportunity cost.
PPF 向外移动表明经济增长，这由生产要素数量或质量的提高所引起。技术进步或劳动力增加是典型的驱动因素。在现有资源和技术条件下，PPF 之外的点目前是无法达到的。PPF 向外弯曲的形状反映了机会成本递增原则。
4. Demand: The Law and the Curve | 需求：定律与曲线
The law of demand states that, ceteris paribus (all other things being equal), as the price of a good or service increases, the quantity demanded decreases. Conversely, when price falls, quantity demanded rises. This inverse relationship creates a downward-sloping demand curve.
需求定律指出，在其他条件不变的情况下，当一种商品或服务的价格上升时，需求量下降。反之，当价格下降时，需求量上升。这种反向关系形成了一条向下倾斜的需求曲线。
A movement along the demand curve occurs solely due to a change in the price of the product itself. A shift of the entire demand curve happens when any non-price determinant changes. Key shift factors include changes in income, prices of related goods (substitutes and complements), tastes, advertising, demographics and expectations.
仅仅由于产品本身价格的变化而引起的变动是沿着需求曲线的移动。当任何非价格决定因素发生变化时，整条需求曲线会发生平移。关键的平移因素包括收入变化、相关商品（替代品和互补品）的价格变化、消费者偏好、广告、人口统计特征和预期。
D(P) → Qd ↓ when P ↑ (Ceteris Paribus)
在其他条件不变时，价格 P ↑ 导致需求量 Qd ↓
5. Supply: The Law and the Curve | 供给：定律与曲线
The law of supply establishes a direct relationship between price and quantity supplied. As the price of a product increases, producers are willing to supply more of it, motivated by the potential for higher profits. This results in an upward-sloping supply curve.
供给定律确立了价格与供给量之间的正比关系。随着产品价格上升，受潜在更高利润的驱动，生产者愿意供给更多数量。这形成了一条向上倾斜的供给曲线。
A movement along the supply curve is triggered exclusively by a change in the good's own price. Shifts of the supply curve stem from changes in conditions of supply. Important shift determinants include changes in production costs (wages, raw materials), technological progress, indirect taxes, subsidies, weather conditions and the number of sellers in the market.
沿着供给曲线的移动完全由商品自身价格的变化引发。供给曲线的平移源于供给条件的变化。重要的平移决定因素包括生产成本（工资、原材料）的变化、技术进步、间接税、补贴、天气状况以及市场上卖家的数量。
S(P) → Qs ↑ when P ↑ (Ceteris Paribus)
在其他条件不变时，价格 P ↑ 导致供给量 Qs ↑
6. Market Equilibrium and Price Mechanism | 市场均衡与价格机制
Equilibrium occurs at the price where the quantity demanded equals the quantity supplied. At this intersection, there is no tendency for change because the plans of consumers and producers are perfectly aligned. The market is said to clear, with no excess demand (shortage) or excess supply (surplus) remaining.
均衡发生在需求量等于供给量的价格水平上。在这一点上，由于消费者和生产者的计划完美匹配，没有发生变化的趋势。市场此时出清，不存在超额需求（短缺）或超额供给（过剩）。
When the market price is set above equilibrium, a surplus emerges and firms may lower prices to clear excess stock. When the price is below equilibrium, a shortage results and consumers bid up the price. This automatic adjustment through the price mechanism rations scarce resources and signals where resources should be allocated, thus answering the fundamental economic questions.
当市场价格设定在均衡水平之上时，会出现过剩，企业可能会降低价格以清理多余的库存。当价格低于均衡水平时，会出现短缺，消费者会抬高价格。这种通过价格机制进行的自动调节配给了稀缺资源，并发出资源应该配置到何处的信号，从而回答了基本经济问题。
7. Price Elasticity of Demand (PED) | 需求的价格弹性
Price Elasticity of Demand measures the responsiveness of quantity demanded to a change in price. It is calculated using the percentage change in quantity demanded divided by the percentage change in price. The PED coefficient is usually negative, reflecting the law of demand, but by convention economists often ignore the minus sign and refer to its absolute value.
需求的价格弹性衡量需求量对价格变化的反应程度。它的计算方法是需求量的百分比变化除以价格的百分比变化。PED 系数通常为负值，这反映了需求定律，但按照惯例，经济学家通常忽略负号而取其绝对值。
PED = %ΔQd ÷ %ΔP
需求的价格弹性 = 需求量的百分比变化 ÷ 价格的百分比变化
Price elastic demand (PED > 1): Quantity demanded changes more than proportionately to price changes. / 价格弹性需求 (PED > 1)：需求量变化的比例大于价格变化的比例。
Price inelastic demand (PED < 1): Quantity demanded changes less than proportionately. / 价格无弹性需求 (PED < 1)：需求量变化的比例小于价格变化的比例。
y elastic demand (PED = 1): Quantity demanded changes in exact same proportion as price. / 单位弹性需求 (PED = 1)：需求量与价格以完全相同的比例变化。
8. The Relationship Between PED and Total Revenue | PED 与总收入的关系
Total revenue is the total income a firm receives from selling its products, calculated as price multiplied by quantity sold. The impact of a price change on total revenue depends entirely on the PED of the product. This relationship is crucial for a firm's pricing decisions.
总收入是一家公司销售其产品所获得的总收入，计算公式为价格乘以销售数量。价格变动对总收入的影响完全取决于该产品的 PED。这种关系对于企业的定价决策至关重要。
Total Revenue (TR) = Price (P) × Quantity (Q)
总收入 (TR) = 价格 (P) × 数量 (Q)
If demand is elastic, raising price will decrease total revenue. / 如果需求富有弹性，提高价格将减少总收入。
If demand is inelastic, raising price will increase total revenue. / 如果需求缺乏弹性，提高价格将增加总收入。
If demand is unitary elastic, a change in price leaves total revenue unchanged. / 如果需求具有单位弹性，价格变化不会影响总收入。
9. Costs of Production: Fixed, Variable and Total | 生产成本：固定成本、可变成本和总成本
In the short run, firms face two distinct types of costs. Fixed costs do not vary with the level of output produced; they must be paid even if output is zero. Variable costs change directly with the level of production. Total cost is the sum of all fixed and variable costs incurred at a given output level.
在短期内，企业面临两种不同的成本类型。固定成本不随产出水平变化；即使产量为零也必须支付。可变成本直接随生产水平变化。总成本是在给定产出水平下发生的所有固定成本和可变成本的总和。
Total Cost (TC) = Fixed Cost (FC) + Variable Cost (VC)
总成本 (TC) = 固定成本 (FC) + 可变成本 (VC)
Average total cost is calculated by dividing total cost by the quantity of output. It represents the cost per unit produced. Understanding average cost helps a firm determine whether it is making a profit or a loss per unit.
平均总成本的计算方法是总成本除以产出数量。它代表每单位产出的成本。了解平均成本有助于企业判断其每单位是盈利还是亏损。
Average Total Cost (ATC) = TC ÷ Q
平均总成本 (ATC) = 总成本 (TC) ÷ 数量 (Q)
10. Revenue, Profit and Loss | 收入、利润与亏损
Profit is the financial reward for risk-taking and enterprise. It is the difference between the total revenue a firm earns from sales and the total costs it incurs in production. A positive difference indicates a profit, a negative difference represents a loss, and a zero difference is the break-even point.
利润是对承担风险和企业家才能的财务回报。它是企业从销售中获得的总收入与它在生产中产生的总成本之间的差额。正差额表示盈利，负差额代表亏损，零差额则是收支平衡点。
Profit/Loss = Total Revenue (TR) − Total Cost (TC)
利润/亏损 = 总收入 (TR) − 总成本 (TC)
ng the firm covers all its costs but makes neither a profit nor a loss. Break-even analysis is a fundamental tool used by entrepreneurs to plan the minimum sales volume required to avoid a loss. It links closely to margin of safety calculations.
收支平衡发生在总收入等于总成本时，意味着企业覆盖了所有成本，但既不盈利也不亏损。盈亏平衡分析是企业家用来规划避免亏损所需的最低销售量的基本工具。它与安全边际的计算密切相关。
11. Key Macroeconomic Indicators | 关键宏观经济指标
Gross Domestic Product measures the total value of all final goods and services produced within a country's borders over a specific time period, typically one year. It is the primary indicator used to gauge the size and health of an economy. Changes in GDP indicate economic growth or contraction.
国内生产总值衡量在一个特定时期（通常为一年）内，一国境内生产的所有最终商品和服务的总价值。它是用来衡量经济规模和健康状况的主要指标。GDP 的变化表明经济增长或收缩。
Inflation is the sustained increase in the general price level of goods and services in an economy over time. It erodes the purchasing power of money. The rate of inflation is most commonly measured by the Consumer Prices Index, which tracks a basket of representative goods.
通货膨胀是指一个经济体中商品和服务总体价格水平在一段时间内持续上涨的现象。它侵蚀了货币的购买力。通货膨胀率最常用的衡量指标是消费者价格指数，该指标追踪一篮子代表性商品的价格变动。
Inflation Rate = (CPIcurrent year − CPIprevious year) ÷ CPIprevious year × 100
通货膨胀率 = (当年 CPI − 上年 CPI) ÷ 上年 CPI × 100
Unemployment refers to individuals who are actively seeking work but are unable to find a job. The unemployment rate measures this as a percentage of the total labour force. It serves as a critical indicator of an economy's ability to utilise its human resources fully.
失业指的是那些积极寻找工作但无法找到工作的个人。失业率将其衡量为占总劳动力的百分比。它是衡量经济体充分利用其人力资源能力的一项关键指标。
Unemployment Rate = (Number of Unemployed ÷ Total Labour Force) × 100
失业率 = (失业人数 ÷ 总劳动力) × 100
12. The Economic Cycle and Monetary Policy | 经济周期与货币政策
The economic cycle describes the fluctuating levels of economic activity over time. It typically moves through four distinct phases: boom (peak), downturn (recession), slump (trough) and recovery (expansion). Government policies often aim to smooth these short-term fluctuations to achieve stable growth.
经济周期描述了经济活动水平随时间的波动。它通常经历四个不同的阶段：繁荣（高峰）、下行（衰退）、萧条（谷底）和复苏（扩张）。政府政策通常旨在平滑这些短期波动，以实现稳定增长。
Monetary policy involves adjusting interest rates and the money supply to influence aggregate demand in the economy. Raising interest rates tends to reduce borrowing, consumption and investment, thus cooling an overheating economy. Lowering interest rates stimulates spending and investment to boost a sluggish economy.
货币政策涉及调整利率和货币供应量，以影响经济体中的总需求。提高利率往往会减少借贷、消费和投资，从而为过热的经济降温。降低利率则刺激支出和投资，以提振疲软的经济。
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