📚 Year 9 AQA Economics: Formula & Theorem Quick Reference Handbook | 九年级 AQA 经济：公式定理速查手册
This quick reference handbook brings together all the key formulas, theorems, and relationships you need for Year 9 AQA Economics. Use it to revise and reinforce your understanding of how markets work, how consumers and producers behave, and how economists measure and interpret real-world data. Each section presents a core concept with its formula or statement, followed by concise explanations in both English and Chinese.
这本速查手册汇集了九年级 AQA 经济学课程中所有重要的公式、定理和核心关系。可用于复习巩固你对市场运行、消费者与生产者行为，以及经济学家如何测量和解读现实世界数据的理解。每个部分都会给出核心概念的公式或表述，并附上中英对照的简明解释。
1. The Law of Demand | 需求定律
The law of demand states that, ceteris paribus (all other things being equal), there is an inverse relationship between the price of a good and the quantity demanded. When price rises, quantity demanded contracts; when price falls, quantity demanded extends.
需求定律指出，在其他条件不变的前提下，商品价格与需求量之间呈反向关系。价格上升，需求量减少（收缩）；价格下降，需求量增加（扩张）。
P ↑ → Qd ↓ and P ↓ → Qd ↑ (ceteris paribus)
价格 ↑ → 需求量 ↓ 且 价格 ↓ → 需求量 ↑（其他条件不变）
is typically written as Qd = f(P), showing that quantity demanded is a function of price.
需求也可以通过需求表和向下倾斜的需求曲线来表达。这种关系通常写作 Qd = f(P)，表示需求量是价格的函数。
2. The Law of Supply | 供给定律
The law of supply asserts that, ceteris paribus, the price of a good and the quantity supplied are directly related. Higher prices give producers an incentive to supply more, as profitability tends to rise.
供给定律阐明，在其他条件不变的情况下，价格与供给量呈正向关系。更高的价格激励生产者提供更多产量，因为利润往往随之提高。
P ↑ → Qs ↑ and P ↓ → Qs ↓ (ceteris paribus)
价格 ↑ → 供给量 ↑ 且 价格 ↓ → 供给量 ↓（其他条件不变）
sent the relationship as Qs = f(P), where quantity supplied depends positively on the good's own price.
典型的供给曲线向上倾斜。该关系可表示为 Qs = f(P)，其中供给量正向取决于商品本身的价格。
3. Market Equilibrium | 市场均衡
Market equilibrium occurs at the price where the quantity demanded equals the quantity supplied. At this point, there is no tendency for the price to change, and the market clears.
市场均衡出现在需求量恰好等于供给量的价格水平上。此时，价格没有变动的趋势，市场出清。
Equilibrium condition: Qd = Qs at P = Pe, Q = Qe
均衡条件：需求量 = 供给量 此时 价格 = 均衡价格 Pe，数量 = 均衡数量 Qe
If the market price is above equilibrium, a surplus (excess supply) pushes the price downwards. If the price is below equilibrium, a shortage (excess demand) pushes the price upwards.
若市场价格高于均衡水平，过剩（超额供给）将促使价格下降。若价格低于均衡水平，短缺（超额需求）将推动价格上升。
4. 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 the good's own price. It is calculated as the percentage change in quantity demanded divided by the percentage change in price.
需求的价格弹性衡量需求量对商品自身价格变动的反应程度。其计算方法为需求量的百分比变化除以价格的百分比变化。
PED = %ΔQd / %ΔP
For calculation, use the formula: % change = [(New value – sitive absolute value, but its sign is negative for ordinary goods. Demand is elastic when |PED| > 1, unit elastic when |PED| = 1, and inelastic when |PED| < 1.
计算时使用公式：% 变化 = [（新值 – 原值）/ 原值] × 100。PED 通常用正数绝对值表示，但普通商品的弹性本身为负值。当 |PED| > 1 时需求富有弹性，|PED| = 1 时为单位弹性，|PED| < 1 时为缺乏弹性。
5. Income Elasticity of Demand (YED) | 需求的收入弹性
Income elasticity of demand measures the responsiveness of demand for a good to a change in consumers' income. It is the percentage change in quantity demanded divided by the percentage change in income.
需求的收入弹性衡量商品需求量对消费者收入变动的反应程度，其值为需求量的百分比变化除以收入的百分比变化。
YED = %ΔQd / %ΔY
If YED is positive, the good is a normal good (demand rises as income rises). If YED is negative, the good is an inferior good (demand falls as income rises). Normal goods with YED > 1 are luxury goods, while those with 0 < YED < 1 are necessities.
若 YED 为正，则该商品为正常品（收入增加，需求上升）。若 YED 为负，则为低档品（收入增加，需求下降）。正常品中 YED > 1 的是奢侈品，0 < YED < 1 的是必需品。
6. Cross Elasticity of Demand (XED) | 需求的交叉弹性
Cross elasticity of demand measures how the demand for one good responds to a change in the price of another good. It is the percentage change in quantity demanded of good A divided by the percentage change in price of good B.
需求的交叉弹性衡量一种商品的需求对另一种商品价格变动的反应程度。它等于商品 A 需求量的百分比变化除以商品 B 价格的百分比变化。
XED = %ΔQd of good A / %ΔP of good B
If XED is positive, the two goods are substitutes (an increase in the price of B leads to a rise in demand for A). If XED is negative, the goods are complements. An XED close to zero indicates that the goods are unrelated.
若 XED 为正，则两种商品互为替代品（B 的价格上涨导致 A 的需求增加）。若 XED 为负，则为互补品。XED 接近零说明两者无关。
7. Price Elasticity of Supply (PES) | 供给的价格弹性
Price elasticity of supply shows how responsive quantity supplied is to a change in the good's own price. It is the percentage change in quantity supplied divided by the percentage change in price.
供给的价格弹性反映供给量对商品自身价格变动的反应灵敏程度，等于供给量的百分比变化除以价格的百分比变化。
PES = %ΔQs / %ΔP
Supply is elastic when PES > 1, meaning producers can increase output quickly in response to a price rise. Supply is inelastic when PES < 1, indicating that output cannot be easily adjusted. Determinants include time period, spare capacity, and the complexity of production.
当 PES > 1 时供给富有弹性，生产者可迅速增加产量以应对价格上涨。当 PES < 1 时供给缺乏弹性，产量不易调整。影响供给弹性的因素包括时间跨度、剩余产能和生产复杂度。
8. Total Revenue and PED | 总收益与需求价格弹性
Total revenue (TR) is the money a firm receives from selling its goods. It is calculated as the price per unit multiplied by the quantity sold. The impact of a price change on total revenue depends on the price elasticity of demand.
总收益 (TR) 是企业出售商品获得的收入，等于单位价格乘以销售数量。价格变动对总收益的影响取决于需求的价格弹性。
TR = P × Q
Revenue rules:
收益法则：
- When demand is elastic (|PED| > 1): a price decrease raises total revenue, and a price increase lowers total revenue.
- 当需求富有弹性时 (|PED| > 1)：降价会增加总收益，涨价会减少总收益。
- When demand is inelastic (|PED| < 1): a price decrease lowers total revenue, and a price increase raises total revenue.
- 当需求缺乏弹性时 (|PED| < 1)：降价会减少总收益，涨价会增加总收益。
- When demand is unit elastic (|PED| = 1): total revenue stays the same regardless of a price change.
- 当需求为单位弹性时 (|PED| = 1)：价格变动不影响总收益。
9. Costs, Revenue and Profit | 成本、收益与利润
Firms use several cost measures to make production decisions. These formulas are fundamental for understanding how businesses operate.
企业使用多种成本指标做出生产决策，这些公式是理解企业如何运作的基础。
Total Cost (TC) = Total Fixed Cost (TFC) + Total Variable Cost (TVC)
总成本 (TC) = 总固定成本 (TFC) + 总变动成本 (TVC)
Average Total Cost (ATC) = TC / Q | Average Fixed Cost (AFC) = TFC / Q | Average Variable Cost (AVC) = TVC / Q
平均总成本 (ATC) = TC / Q | 平均固定成本 (AFC) = TFC / Q | 平均变动成本 (AVC) = TVC / Q
Marginal Cost (MC) = ΔTC / ΔQ
边际成本 (MC) = ΔTC / ΔQ
Profit is the reward for taking risk. Normal profit is the minimum required to keep the firm operating; supernormal profit is earned when TR exceeds total costs including opportunity cost.
利润是对承担风险的回报。正常利润是维持企业运营所需的最低回报；当总收益超过包含机会成本在内的全部成本时，企业获得超额利润。
Profit (π) = Total Revenue (TR) – Total Cost (TC)
利润 (π) = 总收益 (TR) – 总成本 (TC)
10. Opportunity Cost and the Production Possibility Frontier (PPF) | 机会成本与生产可能性边界
Opportunity cost is the value of the next best alternative foregone when a choice is made. It is a central concept in economics because resources are scarce and choices must be made.
机会成本是做出选择时所放弃的次优选项的价值。由于资源稀缺，必须做出选择，因而机会成本是经济学的核心概念。
Opportunity Cost = Value of the Next Best Alternative Foregone
机会成本 = 所放弃的次优选项的价值
The PPF illustrates the maximum possible combinations of two goods an economy can produce with its current resources and technology. Points inside the curve show inefficiency; points outside are unattainable. Moving along the PPF involves an opportunity cost: increasing the output of one good requires sacrificing some output of the other.
生产可能性边界 (PPF) 展示了一个经济体利用现有资源和技术所能生产的两种商品的最大组合。曲线内部的点表示低效率，外部的点无法达到。沿 PPF 移动意味着机会成本：要增加一种商品的产量，必须牺牲另一种商品的部分产量。
Marginal Opportunity Cost = ΔGoods Sacrificed / ΔGoods Gained
边际机会成本 = 牺牲的商品数量变动 / 获得的商品数量变动
11. Marginal Utility and the Law of Diminishing Marginal Utility | 边际效用与边际效用递减规律
Utility refers to the satisfaction or benefit a consumer derives from consuming a good. Total utility (TU) is the total satisfaction from a given quantity; marginal utility (MU) is the additional satisfaction from consuming one more unit.
效用是指消费者从消费某种商品中获得的满足感或收益。总效用 (TU) 是一定数量带来的总满足感；边际效用 (MU) 是多消费一单位所带来的额外满足感。
Marginal Utility (MU) = ΔTotal Utility (TU) / ΔQuantity (Q)
边际效用 (MU) = Δ总效用 (TU) / Δ数量 (Q)
The law of diminishing marginal utility states that as a consumer eats, drinks, or uses more of a product, the additional satisfaction from each extra unit eventually falls. This helps explain why demand curves slope downwards, because consumers will only buy additional units at lower prices.
边际效用递减规律指出，随着消费者消费越来越多的某种产品，每额外一单位带来的满足感最终会下降。这有助于解释为什么需求曲线向下倾斜——消费者只愿意在更低的价格下购买额外单位。
12. Specialisation, Division of Labour and Productivity | 专业化、劳动分工与生产率
Specialisation occurs when individuals, firms, or regions concentrate on producing a limited range of goods or services. Division of labour breaks the production process into separate tasks, allowing workers to focus on what they do best. Both raise productivity.
专业化是指个人、企业或地区专注于生产有限种类的商品或服务。劳动分工将生产过程分解为独立的任务，使工人能专注于自己最擅长的工作。这两者均能提高生产率。
Productivity = Total Output / Total Input
生产率 = 总产出 / 总投入
Labour productivity can be measured as output per worker or output per hour worked. Higher productivity lowers average costs and can increase the economy's potential output, shifting the PPF outward over time.
劳动生产率可以衡量为每个工人的产出或每小时工作的产出。更高的生产率会降低平均成本，并能增加经济的潜在产出，使 PPF 随时间向外移动。
Capital-intensive production uses more machinery, while labour-intensive production relies more on workers. Both forms of specialisation enable firms to exploit economies of scale.
资本密集型生产更多地使用机器，劳动密集型生产则更多地依赖工人。这两种专业化形式都能让企业利用规模经济。
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