问题 解答题

(本题满分12分) 

已知a∈R,函数f(x)=4x3-2ax+a.

(1)求f(x)的单调区间;

(2)证明:当0≤x≤1时,f(x)+|2-a|>0.

答案

(1)函数f(x)的单调递增区间为

单调递减区间为.(2)见解析。

题目分析:(1)根据函数的导数符号与函数单调性的关系来判定求解其单调区间。

(2)要证明不等式恒成立问题,那么要转化为函数的最值问题来处理即可或者构造函数求解函数的 最小值大于零得到。

解:

(1)由题意得f′(x)=12x2-2a.

当a≤0时,f′(x)≥0恒成立,此时f(x)的单调递增区间为(-∞,+∞).

当a>0 时,f′(x)=12,此时

函数f(x)的单调递增区间为

单调递减区间为.

(2)由于0≤x≤1,故

当a≤2时,f(x)+|a-2|=4x3-2ax+2≥4x3-4x+2.

当a>2时,f(x)+|a-2|=4x3+2a(1-x)-2≥4x3+4(1-x)-2=4x3-4x+2.

设g(x)=2x3-2x+1,0≤x≤1,则g′(x)=6x2-2=6,于是

 

x

 

0

 
 -0+ 
1减函数极小值增函数1
所以g(x)min=g=1->0.

所以当0≤x≤1时,2x3-2x+1>0.

故f(x)+|a-2|≥4x3-4x+2>0.

点评:对于含有参数的二次不等式问题的求解是解决导数中常见的非常重要的,注意对于开口和判别式的情况进行分类讨论得到结论。

选择题
阅读理解

San Francisco, a leader in urban recycling, is preparing to turn dog waste into energy.

Norcal Waste System Inc., the city’s largest garbage company, plans to test collection carts(回收车)and collection bags in a city-center park which is popular with dog walkers.

A city study found that almost 4 percent of all the garbage picked up at San Francisco homes was from animal waste, Norcal Waste spokesman Robert Reid said. San Francisco has about 120,000 dogs.

“The city asked us to start a program to recycle dog waste in order to cut back adding more waste in landfills(废渣埋填池) “,Reid said.

Dog waste will be poured into a methane digester(沼气池),and the methane it gives off will be collected and burned to make electricity or to heat homes.

“Dogs and cats in the United States produce about 10 million tons of waste a year,” Will Brinton, an environmental scientist said.

“As much as we love them, our pets leave a lot of fertilizer behind them in yards and on the street but that can be a major source of contamination of groundwater,” Brinton said.

European cities such as Zurich, Frankfurt, Munich and Vienna are starting biology programs to turn waste into gas ,he said.

San Francisco runs a great program to recycle bottles, cars, paper and other rubbish and now two-thirds of its garbage needn’t be carried to landfills .The city’s goal is a 75 percent drop by 2010 and zero new waste in landfills by 2020.

小题1:San Francisco will plan to use dog waste for making __________.

A.fertilizer

B.gas

C.electricity

D.methane小题2:What does the underlined word “ contamination” mean?

A.Increase

B.Reduction

C.Flow

D.Pollution小题3:What can we infer from the passage?

A.San Francisco is short of electricity

B.San Francisco has done a lot of in rubbish recycling.

C.Fewer people will keep dogs as pets in San Francisco

D.There will be no rubbish by 2010 in San Francisco小题4:The passage is mainly about_______.

A.San Francisco ‘s new policy for pet keepers

B.San Francisco ‘s new plan for recycling

C.how to keep a city clean

D.how to deal with rubbish