📚 Year 9 AQA Economics: Formula & Theorem Quick Reference Handbook | Year 9 AQA 经济：公式定理速查手册
This quick reference handbook covers the essential formulas and fundamental theorems for Year 9 AQA Economics. It is designed to help you revise key concepts and master simple calculations step by step. Each section explains the economic idea and then presents the relevant formulas or logical rules you need to remember.
这本速查手册涵盖了 Year 9 AQA 经济学的核心公式和基本定理,旨在帮助你逐步复习重要概念并掌握简单的计算。每一部分先解释经济学原理,再列出需要记住的公式或逻辑规则,中英对照便于随时查阅。
1. Scarcity and Opportunity Cost | 稀缺性与机会成本
Scarcity is the fundamental economic problem: unlimited wants but limited resources. Because resources are scarce, every choice involves an opportunity cost – the value of the next best alternative sacrificed.
稀缺性是经济学的基本问题：无限的欲望与有限的资源并存。由于资源稀缺,每一个选择都涉及机会成本——即所放弃的次优选择的价值。
est alternative foregone. There is no complex mathematical formula here, but the logic is: if you spend £ n a book, the opportunity cost is the meal or cinema ticket you could have bought instead.
机会成本 = 放弃的次优选择的价值。这里没有复杂的数学公式,但逻辑清晰：如果你花 10 英镑买了一本书,机会成本就是你本可以买的那一顿饭或那张电影票。
2. Production Possibility Frontier (PPF) | 生产可能性边界
A PPF shows the maximum possible output combinations of two goods an economy can produce when all resources are fully and efficiently used. The slope of the PPF represents the marginal rate of transformation (MRT).
生产可能性边界表示当一个经济体的所有资源都得到充分利用并且高效使用时,它所能生产的两种商品的最大产量组合。PPF 的斜率代表边际转换率。
MRT = –ΔY / ΔX
This formula means that to produce one more unit of good X, the economy must sacrifice some amount of good Y. The negative sign reflects the trade‑off nature of the frontier. If the PPF is a straight line, the MRT is constant; if it is curved, the MRT changes as production shifts.
该公式表示,要多生产一单位商品 X,经济体就必须牺牲一定数量的商品 Y。负号反映了边界的取舍性质。如果 PPF 是一条直线,边际转换率保持不变；如果是内凹曲线,边际转换率会随着生产转向而变化。
3. Law of Demand and Demand Function | 需求定律与需求函数
The law of demand states that, ceteris paribus, as the price of a good rises, the quantity demanded falls, and vice versa. This inverse relationship can be expressed as a linear demand function.
需求定律指出,在其他条件不变的情况下,商品价格上升时需求量下降,反之亦然。这种反向关系可以用线性需求函数来表达。
Qd = a – bP
Here Qd is the quantity demanded, P is the price, a is the quantity demanded when the price is zero (the intercept on the quantity axis), and b is the slope which shows how responsive demand is to price changes. The negative sign in front of b indicates the inverse relationship.
其中 Qd 是需求量,P 是价格,a 是价格为零时的需求量（需求量轴上的截距）,b 是斜率,反映需求对价格变化的敏感程度。b 前面的负号体现了反向关系。
4. Law of Supply and Supply Function | 供给定律与供给函数
The law of supply states that, ceteris paribus, as the price of a good rises, the quantity supplied increases, and as the price falls, the quantity supplied decreases. The supply function is usually upward‑sloping.
供给定律指出,在其他条件不变的情况下,商品价格上升时供给量增加,价格下降时供给量减少。供给函数通常向上倾斜。
Qs = c + dP
In this equation, Qs is the quantity supplied, P is the price, c is the quantity that would be supplied if the price were zero (often zero or negative in practice), and d is the positive slope indicating that higher prices encourage more production.
此方程中 Qs 是供给量,P 是价格,c 是价格为零时可能存在的供给量（在实际中通常为零或负值）,d 是正的斜率,表示价格越高生产积极性越大。
5. Market Equilibrium | 市场均衡
Market equilibrium occurs at the price where the quantity demanded equals the quantity supplied. At this price, the market clears and there is no tendency for change.
市场均衡发生在需求量等于供给量的价格水平上。在这一价格下,市场出清,没有自动变化的趋势。
Qd = Qs
To find the equilibrium price and quantity, set the demand function equal to the supply function and solve for P. Then substitute P back into either function to find Q.
要计算均衡价格和均衡数量,令需求函数等于供给函数并解出 P,再将 P 代入任一函数求得 Q。
a – bP = c + dP → P* = (a – c) / (b + d)
This formula gives the equilibrium price. Once you have P*, use Qd = a – bP* or Qs = c + dP* to work out the equilibrium quantity.
这个公式给出了均衡价格。求得 P* 后,再用 Qd = a – bP* 或 Qs = c + dP* 计算出均衡数量。
6. Price Elasticity of Demand (PED) | 需求的价格弹性
Price elasticity of demand measures how responsive the quantity demanded is to a change in price. It helps businesses and governments predict consumer reactions.
需求的价格弹性度量需求量对价格变化的反应程度,有助于企业和政府预测消费者的反应。
PED = (%ΔQd) / (%ΔP)
The symbol Δ means “change in”. If you are given actual numbers, you can use the midpoint formula for a more accurate measure between two points on the demand curve.
符号 Δ 表示“变化量”。如果给出了具体数据,可以使用中点公式来更准确地计算需求曲线上两点之间的弹性。
PED = [(Q₂ – Q₁) / ((Q₂ + Q₁) / 2)] ÷ [(P₂ – P₁) / ((P₂ + P₁) / 2)]
Values of PED interpretation: if |PED| > 1, demand is elastic; if |PED| < 1, demand is inelastic; if |PED| = 1, demand is unit elastic; if |PED| = 0, demand is perfectly inelastic; if |PED| y elastic. Remember that PED is usually negative, but we often look at its absolute value.
PED 取值含义：如果 |PED| > 1,需求富有弹性；若 |PED| < 1,需求缺乏弹性；若 |PED| = 1,需求具有单位弹性；若 |PED| = 0,需求完全无弹性；若 |PED| → ∞,需求完全有弹性。记住 PED 通常为负数,但我们常看其绝对值。
7. Income Elasticity of Demand (YED) | 需求的收入弹性
Income elasticity of demand shows how the quantity demanded changes as consumer income changes. It helps classify goods as normal or inferior.
需求的收入弹性表明需求量如何随消费者收入的变化而变化,有助于将商品分为正常品和低档品。
YED = (%ΔQd) / (%ΔY)
Here Y stands for income. A positive YED means the good is normal (demand rises when income rises). A negative YED means the good is inferior (demand falls when income rises). For normal goods, if YED > 1, the good is a luxury; if 0 < YED < 1, it is a necessity.
这里 Y 表示收入。YED 为正说明该商品是正常品（收入增加时需求上升）；YED 为负说明该商品是低档品（收入增加时需求下降）。对于正常品,如果 YED > 1 为奢侈品,0 < YED < 1 则为必需品。
8. Cross Elasticity of Demand (XED) | 需求的交叉价格弹性
Cross elasticity of demand measures how the quantity demanded of one good (A) responds to a change in the price of another good (B). It identifies substitutes and complements.
需求的交叉价格弹性度量一种商品 (A) 的需求量如何随另一种商品 (B) 价格的变化而变化,借此判断替代品与互补品。
XED = (%ΔQd of good A) / (%ΔP of good B)
If XED is positive, goods A and B are substitutes (e.g. tea and coffee). If XED is negative, they are complements (e.g. printers and ink cartridges). A XED close to zero suggests the goods are unrelated.
如果 XED 为正,商品 A 与 B 互为替代品（例如茶和咖啡）；如果 XED 为负,则互为互补品（例如打印机和墨盒）。XED 接近于零表明两种商品无关。
9. Costs, Revenue and Profit | 成本、收益与利润
Firms need to understand their revenues, costs and profit to make sound business decisions. The simplest profit equation lies at the heart of financial planning.
企业需要理解收入、成本和利润,才能做出稳健的商业决策。最基本的利润等式是财务规划的核心。
Total Revenue (TR) = Price (P) × Quantity sold (Q)
nds on the selling price and the number of units sold. If a business sells 100 bouquets at £12 each, TR = £1 200.
这个简单的公式表明,总收入取决于售价和销售数量。如果一家企业以 12 英镑的价格卖出 100 束花,总收入就是 1 200 英镑。
Profit (π) = Total Revenue (TR) – Total Cost (TC)
Total cost includes all fixed costs (e.g. rent) and variable costs (e.g. raw materials). A positive profit means the business is making money; a negative profit is a loss. This basic idea is essential for understanding business objectives and supply decisions.
总成本包括所有固定成本（如租金）和可变成本（如原材料）。正的利润表示企业盈利,负的利润即为亏损。这个基本概念对于理解企业目标与供给决策至关重要。
10. Inflation and the Quantity Theory of Money | 通货膨胀与货币数量理论
Inflation is a sustained rise in the general price level. A simple way to understand the link between money supply and inflation is the quantity theory of money, expressed by the Fisher equation.
通货膨胀是指一般物价水平的持续上涨。理解货币供应量与通货膨胀之间关系的一个简单方法是货币数量理论,由费雪方程表示。
MV = PT
umber of transactions or real output. An alternative form is MV = PY, where Y is real GDP.
其中 M 是货币供应量,V 是流通速度（货币转手的次数）,P 是平均价格水平,T 是交易数量或实际产出。另一种表达式为 MV = PY,其中 Y 代表实际 GDP。
The equation suggests that if V and T (or Y) are relatively stable, an increase in M will lead to a proportionate increase in P, i.e. inflation. This helps explain why central banks control money supply growth.
该等式表明,如果 V 和 T（或 Y）相对稳定,那么 M 的增加会导致 P 按比例上升,也就是通胀。这有助于解释为什么央行要控制货币供应增速。
Inflation Rate = [(P₂ – P₁) / P₁] × 100%
This simple percentage change formula lets you calculate the rate of inflation when you know the price level in two different time periods. It is widely used to measure changes in the Consumer Price Index (CPI).
这个简单的百分比变化公式可用于计算两个不同时期之间的通货膨胀率,常用来衡量消费者价格指数 (CPI) 的变化。
Published by TutorHao | Economics Revision Series | aleveler.com
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