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问题 解答题

已知点P为圆C：（x+1）2+y2=9上一点，A（1，0）为圆C内一点，线段AP的中垂线交半径CP于点M，求点M的轨迹方程.

答案

M的轨迹方程为+=1.

如图所示,由于M是AP中垂线上的点，

∴|MP|=|MA|.

∴|MC|+|MA|=|MC|+|MP|=R=3.

由椭圆定义可知

点M的轨迹为以C(-1,0)、A（1，0）为两焦点的椭圆，且半焦距c=1，a=.

∴b2=.

∴M的轨迹方程为+=1.

单项选择题

在这条公路上行驶的最高速度不能超过多少？（）

A．30公里/小时

B．40公里/小时

C．50公里/小时

D．70公里/小时
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单项选择题

Not everyone in the world requires the same amount of living space. The amount of space a person needs around him is a cultural difference, not an economic one. Knowing your own psychological space needs is important because they ply affect your choices, including, for example, the number of bedrooms in the home. If you were brought up in a two child family and both you and your sister or brother had your own bedrooms, the chances are if you have two children or more, that you also will offer separate bedrooms for them. In America, for example, they train people to want to have their own rooms by giving them their own rooms when they are babies. This is very unusual in the world. In many other countries, the baby sleeps in the same bed with his parents or in bed near them.
The space in the home also shows a lot about psychological space needs. Some families gather closer to each other and the size of their house has nothing to do with it. Others have separate little corners where family members go to be alone.
Although it is true that psychological space needs are not decided by economic reasons, they sometimes have to be changed a little because of economic pressure. It is almost impossible, however, to completely change your psychological space needs.

Which of the following is true according to the passage

A．Americans are trained to live in large rooms at birth.
B．Economic situation decides one’s amount of space needs.
C．People in various countries demand different psychological space.
D．Knowing your psychological space needs is important, as it affects your future.
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