📚 Year 8 Edexcel Economics: Formula & Theorem Quick Reference Guide | 爱德思经济：公式定理速查手册
Welcome to your go-to revision companion for Year 8 Edexcel Economics. This guide brings together all the essential formulas, theorems, and key relationships you need to master the subject. From opportunity cost to market equilibrium, use these quick references to boost your confidence and prepare effectively for tests and end-of-year examinations. Keep it handy and revisit it regularly to strengthen your economic reasoning and calculation skills.
欢迎使用这本针对八年级爱德思经济学的速查手册。我们为你整理了所有关键的公式、定理和核心关系，帮助你轻松掌握这门学科。从机会成本到市场均衡，用这些速查要点提升你的信心，有效备考测验和期末考试。随身携带、经常翻阅，不断加强经济推理与计算能力。
1. The Fundamental Economic Problem: Scarcity | 基本经济问题：稀缺性
Scarcity means that unlimited wants exceed limited resources. It forces every economy to answer three questions: What to produce? How to produce? For whom to produce? The concept of scarcity underlies every decision and trade-off in Economics.
稀缺性意味着无限的欲望超过了有限的资源。它迫使每个经济体回答三个问题：生产什么？如何生产？为谁生产？稀缺性概念是整个经济学中所有决策和权衡的基础。
- Unlimited wants vs. finite resources = scarcity. / 无限的欲望与有限的资源 = 稀缺。
- Choice must be made → opportunity cost arises. / 必须做出选择 → 产生机会成本。
2. Opportunity Cost | 机会成本
Opportunity cost is the value of the next best alternative forgone when a choice is made. It is not always measured in money; it can be time, enjoyment, or any benefit given up.
机会成本是指做出一种选择时所放弃的次优选择的价值。它不一定用金钱衡量，也可以是时间、享受或任何被放弃的收益。
Opportunity Cost = Value of Next Best Alternative Forgone
机会成本 = 放弃的次优选择的价值
For example, if you spend 10 pounds on a film ticket instead of a meal, the opportunity cost is the enjoyment of the meal. If you choose to study one extra hour, you forgo an hour of gaming.
举例来说，如果你把10英镑花在电影票上而不是一顿饭，机会成本就是那顿饭带来的享受。如果你选择多学习一小时，你就放弃了一小时的游戏时间。
3. Production Possibility Frontier (PPF) | 生产可能性边界
The PPF shows the maximum possible output combinations of two goods an economy can produce with given resources and technology. Points on the curve are efficient; points inside are inefficient; points outside are unattainable. The slope represents opportunity cost.
PPF展示了一个经济体在既定资源和技术下能够生产的两种商品的最大产出组合。曲线上的点是有效率的；曲线内的点效率低下；曲线外的点无法达到。斜率代表机会成本。
- Moving along the PPF: trade-off and opportunity cost. / 沿着PPF移动：权衡和机会成本。
- Shift outward: economic growth through more resources or better technology. / 向外移动：由于更多资源或技术进步带来的经济增长。
4. Law of Demand | 需求定律
The law of demand states that, ceteris paribus, as the price of a good increases, the quantity demanded decreases, and vice versa. The demand curve slopes downwards from left to right.
需求定律指出，在其他条件不变的情况下，商品价格上升，需求量下降，反之亦然。需求曲线从左向右下方倾斜。
Qd = f(P) — inverse relationship
Qd = f(P) — 反向关系
A linear demand function can be written as: Qd = a – ty when price is zero, b reflects the slope (change in quantity per unit change in price).
线性需求函数可以写为：Qd = a – bP，其中a是价格为零时的需求量，b反映斜率（价格每单位变动对应的数量变动）。
5. Law of Supply | 供给定律
The law of supply states that, ceteris paribus, as the price of a good increases, the quantity supplied increases. The supply curve slopes upwards from left to right.
供给定律指出，在其他条件不变的情况下，商品价格上升，供给量增加。供给曲线从左向右上方倾斜。
Qs = f(P) — direct relationship
Qs = f(P) — 正比关系
here c is the quantity supplied when price is zero (often negative, showing minimum price needed), d indicates how responsive supply is to price changes.
线性供给函数：Qs = c + dP，其中c是价格为零时的供给量（通常为负，表明所需的最低价格），d表示供给对价格变化的反应程度。
6. Market Equilibrium | 市场均衡
Market equilibrium occurs where quantity demanded equals quantity supplied. At this point, there is no shortage or surplus, and the market-clearing price is established.
市场均衡出现在需求量等于供给量时。此时既没有短缺也没有过剩，形成市场出清价格。
Qd = Qs → Equilibrium Price (Pe) and Equilibrium Quantity (Qe)
Qd = Qs → 均衡价格 (Pe) 和均衡数量 (Qe)
To find equilibrium algebraically, set demand equal to supply: a – bP = c + dP → solve for P, then substitute back to find Q.
要通过代数求均衡，令需求等于供给：a – bP = c + dP → 解出P，再代回求出Q。
- Price above equilibrium → surplus (Qs > Qd). / 价格高于均衡 → 过剩。
- Price below equilibrium → shortage (Qd > Qs). / 价格低于均衡 → 短缺。
7. Price Elasticity of Demand (PED) | 需求的价格弹性
PED measures the responsiveness of quantity demanded to a change in price. It helps firms predict how total revenue will change with price adjustments.
PED衡量需求量对价格变化的反应程度。它有助于企业预测价格调整时总收入如何变化。
PED = (% Change in Quantity Demanded) / (% Change in Price)
PED = (需求量变动的百分比) / (价格变动的百分比)
Using the midpoint formula for accuracy:
为精确起见，使用中点公式：
PED = (ΔQ / Qavg) / (ΔP / Pavg)
- |PED| > 1 → elastic; total revenue rises when price falls. / 弹性；降价增加总收入。
- |PED| < 1 → inelastic; total revenue rises when price rises. / 缺乏弹性；提价增加总收入。
- |PED| = 1 → unit elastic. / 单位弹性。
8. Price Elasticity of Supply (PES) | 供给的价格弹性
PES measures the responsiveness of quantity supplied to a change in price.
PES衡量供给量对价格变化的反应程度。
PES = (% Change in Quantity Supplied) / (% Change in Price)
PES = (供给量变动的百分比) / (价格变动的百分比)
Key determinants include time period, availability of spare capacity, and ease of switching production. A steeper supply curve indicates lower elasticity.
关键决定因素包括时间长短、闲置产能的可获得性以及转换生产的难易程度。更陡峭的供给曲线表明较低的弹性。
9. Total Revenue and Total Cost | 总收入与总成本
Total revenue (TR) is the money a firm receives from selling its goods. Total cost (TC) combines all fixed and variable costs.
总收入（TR）是企业从销售商品中获得的货币。总成本（TC）包括所有固定成本和可变成本。
TR = Price × Quantity
TR = 价格 × 数量
TC = Total Fixed Cost (TFC) + Total Variable Cost (TVC)
TC = 总固定成本 (TFC) + 总可变成本 (TVC)
Profit (π) is the difference: π = TR – TC. If TR > TC, the firm earns a profit; if TR < TC, it incurs a loss.
利润（π）是两者的差额：π = TR – TC。如果TR > TC，企业获得利润；如果TR < TC，企业亏损。
10. Average and Marginal Cost | 平均成本与边际成本
Average total cost (ATC) shows the cost per unit of output. Marginal cost (MC) is the extra cost of producing one more unit. These concepts help firms decide optimal output.
平均总成本（ATC）反映每单位产量的成本。边际成本（MC）是增加一单位产量所增加的额外成本。这些概念帮助企业决定最佳产量。
ATC = TC / Q
ATC = 总成本 / 产量
MC = ΔTC / ΔQ
MC = 总成本变动 / 产量变动
When MC < ATC, ATC falls; when MC > ATC, ATC rises. The MC curve intersects the ATC curve at its lowest point.
当MC < ATC时，ATC下降；当MC > ATC时，ATC上升。MC曲线与ATC曲线相交于ATC的最低点。
11. Profit Maximisation Rule | 利润最大化法则
where marginal revenue (MR) equals marginal cost (MC). In perfect competition, MR = Price.
经济学家假设企业追求利润最大化。利润最大化的产量出现在边际收益（MR）等于边际成本（MC）时。在完全竞争中，MR = 价格。
Profit Maximisation Condition: MR = MC
利润最大化条件：MR = MC
If MR > MC, producing more adds to profit. If MR < MC, producing less increases profit. This rule applies to all market structures.
如果MR > MC，多生产会增加利润。如果MR < MC，减少产量会增加利润。这一法则适用于所有市场结构。
12. Cost-Benefit Analysis Principle | 成本效益分析原则
Rational choices in economics compare total benefits with total costs. A decision should be taken if the expected marginal benefit (MB) exceeds marginal cost (MC). This applies to consumers, firms, and governments.
经济学中的理性选择会对比总收益与总成本。若预期的边际收益（MB）大于边际成本（MC），就应做出该决策。这适用于消费者、企业和政府。
Decision rule: MB ≥ MC
决策法则：MB ≥ MC
This framework helps explain why students choose to study an extra hour, why firms hire an extra worker, or why governments invest in infrastructure.
这个分析框架有助于解释为什么学生会选择多学习一小时，为什么企业会多雇一个工人，或为什么政府会投资基础设施。
Published by TutorHao | Economics Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图