📚 Year 12 CAIE Economics: Formulas and Theorems Quick Reference Handbook | Year 12 CAIE 经济：公式定理速查手册
This Quick Reference Handbook compiles essential formulas and theorems for Year 12 CAIE Economics, enabling rapid revision and application. Each concept is presented with a formula, explanation, and practical tips to help students master both Micro and Macro topics.
本速查手册汇集了 Year 12 CAIE 经济学核心公式与定理，便于快速复习与应用。每个概念均提供公式、解释与实用提示，帮助学生掌握微观与宏观经济主题。
1. Price Elasticity of Demand (PED) | 需求价格弹性 (PED)
PED = %ΔQd / %ΔP
需求价格弹性 = 需求量变动% ÷ 价格变动%
The percentage change in quantity demanded (%<0x94>Qd) is divided by the percentage change in price (%<0x94>P). Because of the law of demand, PED is normally negative; we often report its absolute value |PED|.
需求量变动百分比（%ΔQd）除以价格变动百分比（%ΔP）。由于需求定律，PED 通常为负值；我们常使用其绝对值 |PED|。
Interpretation of |PED| values:
|PED| 值的解读：
| |PED| > 1 | Elastic demand | 富有弹性 |
| |PED| < 1 | Inelastic demand | 缺乏弹性 |
| |PED| = 1 | Unit elastic | 单位弹性 |
| |PED| = 0 | Perfectly inelastic | 完全无弹性 |
| |PED| → ∞ | Perfectly elastic | 完全弹性 |
Key determinants of PED include the availability of substitutes, the degree of necessity, the proportion of income spent, and the time period.
影响 PED 的关键因素包括替代品的可获得性、必要程度、占收入的比例以及时间周期。
2. Income Elasticity of Demand (YED) and Cross Elasticity of Demand (XED) | 收入需求弹性 (YED) 与交叉需求弹性 (XED)
Income Elasticity of Demand (YED): YED = %ΔQd / %ΔY
收入需求弹性 (YED)：YED = 需求量变动% ÷ 收入变动%
A positive YED indicates a normal good (YED > 0); a negative YED indicates an inferior good (YED < 0).
正的 YED 表示正常品 (YED > 0)；负的 YED 表示低档品 (YED < 0)。
When YED > 1, the good is a luxury; when 0 < YED < 1, it is a necessity.
当 YED > 1，商品为奢侈品；当 0 < YED < 1，则为必需品。
Cross Elasticity of Demand (XED): XED = %ΔQd of good A / %ΔP of good B
交叉需求弹性 (XED)：XED = 商品A 需求量变动% ÷ 商品B 价格变动%
A positive XED signals substitute goods; a negative XED signals complementary goods. An XED close to zero suggests unrelated goods.
正的 XED 表明替代品；负的 XED 表明互补品。XED 接近零则表示无关商品。
3. Price Elasticity of Supply (PES) | 供给价格弹性 (PES)
PES = %ΔQs / %ΔP
供给价格弹性 = 供给量变动% ÷ 价格变动%
PES measures the responsiveness of quantity supplied to a change in price. The sign is usually positive because of the law of supply.
PES 衡量供给量对价格变动的反应程度。由于供给定律，其符号通常为正。
Key factors that affect PES: the length of the production period, spare capacity, the ability to store stocks, and the time frame (momentary, short-run, long-run).
影响 PES 的关键因素：生产周期长度、闲置产能、库存能力以及时间框架（瞬间、短期、长期）。
Supply is elastic when PES > 1, inelastic when PES < 1, and unit elastic when PES = 1.
当 PES > 1 时供给富有弹性，PES < 1 时缺乏弹性，PES = 1 时为单位弹性。
4. Consumer Surplus and Producer Surplus | 消费者剩余与生产者剩余
Consumer surplus (CS) is the area below the demand curve and above the market price, measuring the extra benefit consumers receive.
消费者剩余 (CS) 是需求曲线下方、市场价格上方的区域，衡量消费者获得的额外利益。
For linear demand, it can be approximated as: CS = ½ × (Maximum willingness to pay − Market price) × Quantity
对于线性需求曲线，可近似为：消费者剩余 = ½ × (最高意愿支付价格 − 市场价格) × 数量
Producer surplus (PS) is the area above the supply curve and below the market price, capturing the extra benefit to producers.
生产者剩余 (PS) 是供给曲线上方、市场价格下方的区域，体现生产者获得的额外利益。
Total welfare = CS + PS; a competitive equilibrium maximises total welfare.
总福利 = 消费者剩余 + 生产者剩余；竞争均衡使总福利最大化。
5. Utility Maximisation: Equi-Marginal Principle | 效用最大化：边际效用均等法则
MUx / Px = MUy / Py
商品X的边际效用 / 价格X = 商品Y的边际效用 / 价格Y
A rational consumer allocates income so that the last dollar spent on each good yields the same marginal utility. This ensures maximum total utility subject to the budget constraint I = PxX + PyY.
理性消费者分配收入，使得花在每一种商品上的最后一元带来的边际效用相等。这可在预算约束 I = PxX + PyY 下实现总效用最大化。
If MUx/Px > MUy/Py, the consumer should buy more of X and less of Y until the equality is restored.
若 MUx/Px > MUy/Py，消费者应多买 X 并少买 Y，直至等式成立。
6. Costs of Production | 生产成本
Total Cost (TC) = Total Fixed Cost (TFC) + Total Variable Cost (TVC)
总成本 (TC) = 总固定成本 (TFC) + 总可变成本 (TVC)
Average Fixed Cost (AFC) = TFC / Q
Average Variable Cost (AVC) = TVC / Q
Average Total Cost (ATC) = TC / Q = AFC + AVC
平均固定成本 (AFC) = TFC / 产量
平均可变成本 (AVC) = TVC / 产量
平均总成本 (ATC) = TC / 产量 = AFC + AVC
Published by TutorHao | Year 12 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