理想状态下的市场能够达到高效生产：将总剩余(total surplus)最大化。 但是在现实中的市场并非完美。在本课程中，我们将探索一系列市场存在着缺陷的情形并且理解为什么会出现这些缺陷；同时，我们会了解一些改进措施，比如反托拉斯(antitrust)政策以及其他一些政府的干预措施。 我们会选取日常中的例子——从我们每天购买和享用的货物和服务开始。我们也会在每周的练习里把理论运用到时下大事和政策研讨中。 所有的这些都会使你成为一个可以理解、分析和评价市场结果的，有学识的，有批判精神的思考者。

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From the course by 宾夕法尼亚大学

微观经济学：当市场“失灵”时

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理想状态下的市场能够达到高效生产：将总剩余(total surplus)最大化。 但是在现实中的市场并非完美。在本课程中，我们将探索一系列市场存在着缺陷的情形并且理解为什么会出现这些缺陷；同时，我们会了解一些改进措施，比如反托拉斯(antitrust)政策以及其他一些政府的干预措施。 我们会选取日常中的例子——从我们每天购买和享用的货物和服务开始。我们也会在每周的练习里把理论运用到时下大事和政策研讨中。 所有的这些都会使你成为一个可以理解、分析和评价市场结果的，有学识的，有批判精神的思考者。

From the lesson

Monopoly

A monopoly is a case where there is only one firm in the market. We will define and model this case and explain why market power is good for the firm, bad for consumers. We will also show that society as a whole suffers from the lack of competition.

- Rebecca SteinSenior Lecturer

Economics

[MUSIC]

I'd like us to take a few more minutes discussing why, in the case of monopoly,

the marginal revenue is less than the price.

And let's go through a numeric example.

Suppose we're giving a demand curve quantity equals 150-P,

or the inverse command curve, the way I'm going to draw it,

is price is equal to 150-Q.

So again, this is my demand curve.

The intercept is 150 and it's a straight line with a slope of 1.

And just for the sake of example, suppose we start off with a price of

$100 per unit, which means we're selling 50 units.

And we can find that point along the demand curve.

Here's 100 and here's the quantity of 50 units.

This is a point along the demand curve.

We can go head and calculate the revenue.

100 times 50 is equal to $5,000.

Now suppose the monopolist wants to sell an additional unit.

They cannot sell the additional unit at $100.

We know this from the demand curve, because this point here,

51 and 100, is simply not on the demand curve.

The only way the monopolist can sell one more unit is by lowering the price.

And we can see from the equation that in order to sell 51 units,

the price has to go down to $99.

Well, what would be the revenue in this case?

At the price of $99 we are going to sell 51 units,

and if we multiply 99 by 51 we get 5,049.

What is marginal revenue?

It is the change in revenue from selling the additional unit.

It is the difference between these two revenues, and

we can see that the marginal revenue is equal to $49.

And what I want to emphasize is that this is less than $99, which is the price.

So that is one numerical example.

Let's go ahead and look at a graphic interpretation as well.

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