为什么需求曲线是线性的
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price(dollar) 1 2 3 4 5 demand(kilogram） 10 8 6 4 2
Example
If we use Q to represent the demand, and P to represent price. We can use an equation to show the relation between Q and P. And We call it a Demand Function(需求函数). So Mrs. Brown’s Demand Function is as following:
1. 2.
3.
Mrs. Brown is considering buying some oranges for her family. The following table lists Mrs. Brown’s different demand at different prices. We call it Demand Schedule (需求表)
Q=12-2P （P=1, 2, 3,4, 5）
Again, we can also visualize the relationship between Mrs. Brown’s Demand of oranges and their price by graphing the her Demand Function. And we call this graph Demand Curve (需求曲线)
What comes together with Demand Curve? (补充和需求曲线相关的两个概念)
In most Economics textbooks, the drawing of Demand Curve is actually done via three steps： Demand Schedule 需求表 Demand Function 需求函数 Demand Curve 需求曲线
我们的课本没有提及需求表和需求函数，而是直接给出了需求曲线，这 就难免有些突兀，请注意，其他的众多经济学教材都是经过一个 需求表 > 需求函数 > 需求曲线 的推倒过程的，这样就不会显得那么难理解了。基于以上分析，我们就 容易理解，对应需求概念，在供给的一方，我们有供给表，供给函数 和供给曲线。
Mrs. Brown DemaΒιβλιοθήκη Baidud Curve 12 10
Price(Dollar)
8 6 4 2 0 1 2 3 4 Demand(kilogram) 5
Our text book did not really mention Demand Schedule and Demand Function, that is why it may cause unease to you when the Demand Curve was presented all of a sudden. However, if you read other textbooks, you will understand how demand curve come into appearance. Based on the above analysis, you should understand thr situation on the other side of the coin, we have Supply Schedule, Supply Function and Supply Curve.
Why is Demand Curve a straight line? (为什么需求曲线是直线)
The actual Demand Curve is understandably not a straight line. If we link all the points on the coordinate axes, you will see a very irregular shape, as what I draw on the blackboard. However, since we know the general trend of this curve is going downwards, we can straighten it. In other words, we assume it to be a straight line (well, we do have to make lots of assumptions in Economics) and it will be easy to decide the Demand Function so is the same to Supply Curve. 现实生活中需求受价格影响的复杂性和不规律性，决定了按照 真实情况绘制的需求曲线，是不可能恰好成为一条直线的。如 果我们把坐标轴上的所有需求价格对应点连接起来，你将看到 一个很不规则甚至奇怪的图形。但是，我们知道需求曲线的整 体趋势是下降的，所以我们把本来非直线的需求曲线“直线 化”，话句话说，为了方便研究，我们假设需求和价格是线性 相关的 （经济学本身就是一门建立在众多假设上的科学），这 就意味着对应的需求函数是一次的，同样的道理，我们对供给 曲线也进行这样的处理。
Example
If we use Q to represent the demand, and P to represent price. We can use an equation to show the relation between Q and P. And We call it a Demand Function(需求函数). So Mrs. Brown’s Demand Function is as following:
1. 2.
3.
Mrs. Brown is considering buying some oranges for her family. The following table lists Mrs. Brown’s different demand at different prices. We call it Demand Schedule (需求表)
Q=12-2P （P=1, 2, 3,4, 5）
Again, we can also visualize the relationship between Mrs. Brown’s Demand of oranges and their price by graphing the her Demand Function. And we call this graph Demand Curve (需求曲线)
What comes together with Demand Curve? (补充和需求曲线相关的两个概念)
In most Economics textbooks, the drawing of Demand Curve is actually done via three steps： Demand Schedule 需求表 Demand Function 需求函数 Demand Curve 需求曲线
我们的课本没有提及需求表和需求函数，而是直接给出了需求曲线，这 就难免有些突兀，请注意，其他的众多经济学教材都是经过一个 需求表 > 需求函数 > 需求曲线 的推倒过程的，这样就不会显得那么难理解了。基于以上分析，我们就 容易理解，对应需求概念，在供给的一方，我们有供给表，供给函数 和供给曲线。
Mrs. Brown DemaΒιβλιοθήκη Baidud Curve 12 10
Price(Dollar)
8 6 4 2 0 1 2 3 4 Demand(kilogram) 5
Our text book did not really mention Demand Schedule and Demand Function, that is why it may cause unease to you when the Demand Curve was presented all of a sudden. However, if you read other textbooks, you will understand how demand curve come into appearance. Based on the above analysis, you should understand thr situation on the other side of the coin, we have Supply Schedule, Supply Function and Supply Curve.
Why is Demand Curve a straight line? (为什么需求曲线是直线)
The actual Demand Curve is understandably not a straight line. If we link all the points on the coordinate axes, you will see a very irregular shape, as what I draw on the blackboard. However, since we know the general trend of this curve is going downwards, we can straighten it. In other words, we assume it to be a straight line (well, we do have to make lots of assumptions in Economics) and it will be easy to decide the Demand Function so is the same to Supply Curve. 现实生活中需求受价格影响的复杂性和不规律性，决定了按照 真实情况绘制的需求曲线，是不可能恰好成为一条直线的。如 果我们把坐标轴上的所有需求价格对应点连接起来，你将看到 一个很不规则甚至奇怪的图形。但是，我们知道需求曲线的整 体趋势是下降的，所以我们把本来非直线的需求曲线“直线 化”，话句话说，为了方便研究，我们假设需求和价格是线性 相关的 （经济学本身就是一门建立在众多假设上的科学），这 就意味着对应的需求函数是一次的，同样的道理，我们对供给 曲线也进行这样的处理。