问题 解答题
已知对任意的x>0恒有a1nx≤b(x-1)成立.
(1)求正数a与b的关系;
(2)若a=1,设f(x)=m
x
+n,(m,n∈R),若1nx≤f(x)≤b(x-1)对∀x>0恒成立,求函数f(x)的解析式;
(3)证明:1n(n!)>2n-4
n
(n∈N,n≥2)
答案

(1)设f(x)=alnx-b(x-1),

易知f(1)=0,由已知f(x)≤0恒成立,

所以函数f(x)在x=1处取得最大值.f′(x)=

a
x
-b=
a-bx
x
∴f'(1)=0,∴a=b

又∵a>0,∴f(x)在x=1处取得极大值,符合题意,

即关系式为a=b.(3分)

(2)∵a=1,∴b=1∴lnx≤m

x
+n≤x-1恒成立,

令x=1,有0≤m+n≤0,∴m+n=0(5分)∴m

x
+m≤x-1,

(

x
-1)(
x
+1-m)≥0对∀x>0恒成立,∴须1-m=-1,即m=2∴函数f(x)=2(
x
-1)
(7分)

(3)由(2)知:ln

1
k
2
k
-2=
4
2
k
-2<
4
k
+
k-1
-2=4(
k
-
k-1
)-2(9分)

ln

1
n!
<4[(
n
-
n-1
)+(
n-1
-
n-2
)++(
1
-
0
)]-2n=4
n
-2n

lnn!>2n-4

n
(n∈N,n≥2)(12分)

单项选择题 B型题
写作题

第二节 读写任务(共1小题,满分25分)

阅读下面的短文,然后按照要求写一篇150词左右的英语短文。

Everyone has an experience they would rather forget. Some are embarrassing, some are moving, and some teach us a lesson. Here is a story of mine.

Last Sunday I went fishing. After setting up my fishing rod(钓鱼竿) with bait(钓鱼的饵), I sat down on the bank of the lake. But two hours later, I didn’t catch any fish. I got very angry and began to pack up my stuff(收拾东西), preparing to go back home.

Just then, I saw an old man sitting near me. To my surprise, his basket was full of fish, so I went over to him, wanting to know why. “Excuse me, but how long have you sat here?” I asked. “About four hours,” he answered. “Four hours?” I could believe my ears. “Yes. It’s very important to be patient,” the old man said. “ Don’t consider fishing a tiring sport. Just enjoy it.” Suddenly, I understand what he said. I must learn to be patient. Then I sat there and waited for fish patiently. I felt a fish touch the bait, but I didn’t move and waited for the right moment to reel it in(卷收钓鱼线). At last, I caught it. This made me very happy. In the following six hours, I caught over 10 fish.

On my way home, I thought what had happened on the bank. I gradually realized that the secret of success was patience.

[写作内容]

1. 以约30个词概括短文的要点;

2. 然后以约120个词写一篇记叙文,描写你认识到耐心的重要性的一次经历,

并包括以下要点:

A). 叙述你认识到耐心的重要性的一次真实或虚构的经历;

B)你是如何认识到耐心的重要性的;

C)耐心对你的生活、学习有什么影响。

[写作要求]

可以参照阅读材料的篇章结构,组织故事,但不得直接引用原文中的句子;标题自定。

[评分标准]  

概括准确,语言规范,内容合适,篇章连贯。