题干

已知函数f(x)=alnx﹣x+
1
x
,其中a>0

(Ⅰ)若f(x)在(2,+∞)上存在极值点,求a的取值范围;

(Ⅱ)设x1∈(0,1),x2∈(1,+∞),若f(x2)﹣f(x1)存在最大值,记为M(a).则a≤e+

1
e
时,M(a)是否存在最大值?若存在,求出最大值;若不存在,请说明理由.
上一题 下一题 0.0难度 选择题 更新时间:2015-07-21 05:26:31

答案(点此获取答案解析)

解:(Ⅰ)f′(x)=
a
x
﹣1﹣ 1x2

同类题2

阅读下列短文,根据短文内容,从短文后各题所给的A、B、C、D四个选项中,选择最佳选项。

                                                                                       Bags of Love

      Last year, I worked in a middle school near my mother's house, and I stayed with her for a month. During that time, I helped her do some

 housework and buy some food.

      After the first week, I noticed that the food was eaten up very quickly. Then I began keeping an eye on my mum. To my surprise, I found

that she would put some of the food into a paper bag and go out with it at about nine every morning. And finally, I decided to follow her. I saw her taking the food to the street children. She would also spend a lot of time talking and playing with them.

      One day, I talked to a neighbour and found out that my mum was well-known in the area. The children were very friendly with her and even thought of her as their own mother. Then it hit me – why wouldn't she want to tell me about it? Was she worried that I would stop buying food if I found out?

  When my mum got home, I gave her a big hug (拥抱). I told her she didn't need to keep it a secret from me. And she told me something about the children. Some of them lived with an old lady in a small house. Others slept on the street. For years, she was helping the poor street children by giving them food. After she told me everything, I was so moved by how selfless (无私的) she was. She helped others in need. As her son, I was so proud of my mum.

      I continued to buy food for my mum after that. But I always added one more bag for her other children.