📚 Year 8 CIE Economics: Formula & Theorem Quick-Reference Handbook | 8年级 CIE 经济：公式定理速查手册
This handbook is designed to help Year 8 CIE Economics students quickly review the key formulas, definitions, and fundamental theorems needed for their course. It pairs every concept in English and Chinese so that you can master the essential building blocks of economic thinking.
本手册旨在帮助8年级 CIE 经济学生快速复习课程所需的关键公式、定义和基本定理。每个概念都配有中英双语解释，帮助你掌握经济思维的核心模块。
1. The Basic Economic Problem: Scarcity | 基本经济问题：稀缺性
The fundamental economic problem is scarcity: unlimited human wants confront limited resources. This forces individuals, businesses, and governments to make choices.
基本经济问题是稀缺性：无限的人类欲望面对有限的资源。这迫使个人、企业和政府做出选择。
ources are scarce, every decision to use them in one way means giving up the chance to use them in another.
一条核心定理如下：稀缺性 → 选择 → 机会成本。因为资源是稀缺的，每一项使用资源的决策都意味着放弃了将它们用于其他用途的机会。
2. Opportunity Cost Formula & Calculation | 机会成本公式与计算
Opportunity Cost = Value of the Next Best Alternative Forgone
机会成本 = 放弃的次优选择的价值
Opportunity cost is not simply the sum of all alternatives; it is specifically the benefit lost from the single next best option. It highlights the true cost of any choice.
机会成本并非所有选项的总和，而是特指失去了的次优选择所带来的收益。它揭示了任何选择的真实成本。
For instance, if a student has one hour and chooses to study Economics instead of playing football, the opportunity cost is the enjoyment and fitness gain from playing football, not all other possible activities.
例如，如果一名学生有一小时时间，选择学习经济而不是踢足球，机会成本就是踢足球所带来的快乐和健康收益，而不是所有其他活动的总和。
3. Factors of Production | 生产要素
Production of goods and services requires four factors of production: Land (natural resources), Labour (human effort), Capital (man‑made goods used in production), and Enterprise (the entrepreneur who organises the other three and takes risks).
商品与服务的生产需要四种生产要素：土地（自然资源）、劳动力（人力）、资本（用于生产的人造物品）和企业家才能（组织其他要素并承担风险的企业家）。
p: Output = f(Land, Labour, Capital, Enterprise). Returns to these factors generate income – rent, wages, interest, and profit.
生产过程可概括为：产出 = 函数(土地, 劳动力, 资本, 企业家才能)。对这些要素的回报产生了收入——地租、工资、利息和利润。
4. Demand and the Law of Demand | 需求与需求定律
The Law of Demand: When the price of a good rises, the quantity demanded falls, ceteris paribus.
需求定律：在其他条件不变的情况下，一种商品价格上升，其需求量下降。
This inverse relationship creates a downward‑sloping demand curve. Shifts in demand occur when non‑price determinants change, such as consumer income, tastes, or the prices of substitutes and complements.
这种反向关系形成了一条向右下方倾斜的需求曲线。当非价格决定因素（如消费者收入、偏好、替代品或互补品价格）发生变化时，需求曲线会发生移动。
5. Supply and the Law of Supply | 供给与供给定律
The Law of Supply: When the price of a good rises, the quantity supplied increases, ceteris paribus.
供给定律：在其他条件不变的情况下，一种商品价格上升，其供给量增加。
Higher prices offer greater potential profit, motivating producers to increase output. The supply curve slopes upward. Supply can shift due to changes in production costs, technology, taxes, subsidies, or the number of sellers.
较高的价格带来更高的潜在利润，激励生产者扩大产出。供给曲线向右上方倾斜。生产成本、技术、税收、补贴或卖者数量的变化会导致供给曲线移动。
6. Market Equilibrium | 市场均衡
Equilibrium Price (Pₑ) occurs where Quantity Demanded (Qd) = Quantity Supplied (Qs)
均衡价格（Pₑ）出现在需求量等于供给量之处。
At the equilibrium price, the market clears: there is no surplus (excess supply) and no shortage (excess demand). If the market price is above Pₑ, a surplus pushes the price down; if below Pₑ, a shortage pushes the price up.
在均衡价格下，市场出清：没有过剩（超额供给），也没有短缺（超额需求）。若市价高于Pₑ，过剩会促使价格下降；若低于Pₑ，短缺会推动价格上升。
7. Price Elasticity of Demand – Basic Concept | 需求价格弹性 – 基本概念
Price Elasticity of Demand (PED) = % Change in Quantity Demanded ÷ % Change in Price
需求价格弹性 (PED) = 需求量变化百分比 ÷ 价格变化百分比
If PED > 1, demand is elastic (consumers are very responsive to price changes). If PED < 1, demand is inelastic (consumers are less responsive). Necessities and goods with few substitutes tend to be inelastic.
若PED > 1，需求富有弹性（消费者对价格变化反应灵敏）；若PED < 1，需求缺乏弹性。必需品和替代品较少的商品往往缺乏弹性。
8. Total Revenue and Total Cost | 总收益与总成本
Total Revenue (TR) = Price (P) × Quantity Sold (Q)
总收益 = 价格 × 销售量
Total Cost (TC) = Fixed Costs (FC) + Variable Costs (VC)
总成本 = 固定成本 + 可变成本
Fixed costs do not change with output (e.g., rent), while variable costs rise with production (e.g., raw materials). These two measures form the basis for profit calculation.
固定成本不随产量变化（如租金），可变成本随着产量增加而增加（如原材料）。这两个指标是计算利润的基础。
9. Profit Formula and Average Cost | 利润公式与平均成本
Profit = Total Revenue − Total Cost
利润 = 总收益 − 总成本
Average Cost (AC) = Total Cost ÷ Quantity
平均成本 = 总成本 ÷ 产量
When TR > TC, the firm earns a positive economic profit. AC helps determine the cost per unit and, together with price, shows the profit margin on each item sold.
当总收益大于总成本时，企业获得正经济利润。平均成本揭示了单位成本，与价格结合可以显示每件商品的利润空间。
10. Government Budget: Revenue and Expenditure | 政府预算：收入与支出
Budget Balance = Tax Revenue − Government Spending
预算余额 = 税收收入 − 政府支出
tax revenue equals spending. A surplus occurs when revenue > spending; a deficit occurs when spending > revenue. Direct taxes (e.g., income tax) and indirect taxes (e.g., VAT) are key government revenue tools.
平衡预算（余额为零）意味着税收等于支出。盈余代表收入大于支出；赤字代表支出大于收入。直接税（如所得税）和间接税（如增值税）是关键的政府收入工具。
11. Economic Growth and GDP per Capita | 经济增长与人均国内生产总值
GDP per Capita = Gross Domestic Product (GDP) ÷ Population
人均GDP = 国内生产总值 ÷ 人口
Economic growth is measured as the percentage increase in a nation's total output over time. GDP per capita gives an average output per person and is a widely used indicator of living standards.
经济增长以一国总产出在一定时期内的百分比增长来衡量。人均GDP给出了人均产出的平均值，是广泛使用的生活水平指标。
12. Key Formula Summary | 关键公式总结
The following table collects the most essential formulas for quick revision. Use it as a checklist before your assessments.
下表汇总了最重要的公式，用于考前快速复习。可将其用作核对清单。
| Formula (English) | 公式（中文） |
|---|---|
| Opportunity Cost = Next best alternative forgone | 机会成本 = 次优选择的价值 |
| TR = P × Q | 总收益 = 价格 × 数量 |
| TC = FC + VC | 总成本 = 固定成本 + 可变成本 |
| Profit = TR − TC | 利润 = 总收益 − 总成本 |
| AC = TC ÷ Q | 平均成本 = 总成本 ÷ 产量 |
| PED = %ΔQd ÷ %ΔP | 需求价格弹性 = 需求量变动% ÷ 价格变动% |
| Budget Balance = Tax Revenue − Government Spending | 预算余额 = 税收 − 政府支出 |
| GDP per Capita = GDP ÷ Population
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