搜题请搜索小程序“爱下问搜题”
问题 选择题

已知定义在实数集R上的函数f（x）满足f（1）=2，且f（x）的导数f'（x）在R上恒有f'（x）＜1（x∈R），则不等式f（x）＜x+1的解集为（　　）

A．（1，+∞）

B．（-∞，-1）

C．（-1，1）

D．（-∞，-1）∪（1，+∞）

答案

令g（x）=f（x）-x-1，

∵f′（x）＜1（x∈R），

∴g′（x）=f′（x）-1＜0，

∴g（x）=f（x）-x-1为减函数，

又f（1）=2，

∴g（1）=f（1）-1-1=0，

∴不等式f（x）＜x+1的解集⇔g（x）=f（x）-x-1＜0=g（1）的解集，

即g（x）＜g（1），又g（x）=f（x）-x-1为减函数，

∴x＞1，即x∈（1，+∞）．

故选A．

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.
查看答案
填空题

电流的实际方向是指（）运动的方向或（）运动的反方向。
查看答案