问题 解答题
设函数f(x)=px-
q
x
-2lnx
,且f(e)=qe-
p
e
-2
,其中p≥0,e是自然对数的底数.
(1)求p与q的关系;
(2)若f(x)在其定义域内为单调函数,求p的取值范围.
(3)设g(x)=
2e
x
.若存在x0∈[1,e],使得f(x0)>g(x0)成立,求实数p的取值范围.
答案

(1)由题意,∵函数f(x)=px-

q
x
-2lnx,且f(e)=qe-
p
e
-2
,∴(p-q)(e+
1
e
)=0

e+

1
e
≠0,∴p-q=0,∴p=q

(2)由(1)知,f(x)=px-

p
x
-2lnx,求导函数,可得f′(x)=
px2-2x+p
x2

当p=0时,f′(x)=-

2
x
<0,所以f(x)在其定义域(0,+∞)内为单调减函数

当p>0时,要使f(x)在其定义域(0,+∞)内为单调函数,由于h(x)=px2-2x+p图象为开口向上的抛物线,所以只需h(x)在(0,+∞)内满足h(x)≥0恒成立

函数h(x)=px2-2x+p的对称轴为x=

1
p
∈(0,+∞),∴h(x)min=p-
1
p

∴只需p-

1
p
≥0,∵p>0,∴p≥1

综上所述,p的取值范围为{0}∪[1,+∞)

(3)∵g(x)=

2e
x
在[1,e]上是减函数,

∴x=e时,g(x)min=2;x=1时,g(x)max=2e,即g(x)∈[2,2e]

①当p=0时,由(2)知f(x)在[1,e]上是减函数,∴f(x)min=f(1)=0,不合题意;

②当p≥1时,由(2)知f(x)在[1,e]上是增函数,f(1)=0<2,

g(x)=

2e
x
在[1,e]上是减函数,故只需f(x)max>g(x)min(x∈[1,e]),

∵f(x)max=f(e)=p(e-

1
e
)-2,g(x)min=2,

∴p(e-

1
e
)-2>2,∴p>
4e
e2-1

③当0<p<1时,由x∈[1,e],x-

1
x
≥0,

由(2)知当p=1时,f(x)在[1,e]上是增函数,f(x)=p(x-

1
x
)-2lnx≤x-
1
x
-2lnx
e-
1
e
-2<
2,不合题意

综上,实数p的取值范围是(

4e
e2-1
,+∞).

单项选择题
阅读理解

Hunting with birds is a very old sport. In some countries the golden eagle is used for hunting wild animals. They are used for hunting foxes and wolves.

Training an eagle to hunt takes a long time. Hunters catch young eagles in nets made of hair. After being trained the eagle is taken to a field. A blindfold over the bird’s eyes keeps it quiet until the hunter is ready.

The eagle sits in the arm of the hunter. The hunter’s arm is covered with a long, special glove to protect it from the sharp claws of the bird. In the field, as soon as the hunter sees a fox or a wolf, he removes the blindfold. The eagle quickly flies into the air and began to look for the wild animal.

The eagle sees the animal and catches it with claws like steel. Its beak and claws are strong enough to hold the animal. Usually, the bird carries the animal back to the hunter. Sometimes fast animals with good eyes can get away.

61.A hunting eagle is trained when_________.

A.it is still young          B.it is taken to a field

C.its eyes are covered with a blindfold

D.the hunter is ready

62.Hunters use nets made of hair to ________.

A.train young foxes     B.catch young wolves

C.train young eagles    D.catch young eagles

63.The trained eagle_______.

A.carries the hunter home

B.wears a blindfold when hunting an animal

C.is covered with a long, special glove

D.has strong claws like steel

64.A hunter wears a special glove to _______.

A.protect his arm from the sharp claws of a trained eagle

B.protect his arm from the sharp claws of a young fox

C.protect his arm from the sharp claws of a young wolf

D.protect his arm from the sharp claws of wild animals

65.According to the text, which of the following is true?

A.Fast animals with sharp eyes are sometimes difficult to catch

B.As soon as the blindfold is removed, the eagle flies into a tree

C.Hunters always blindfold young eagles before training them.

D.Sometimes hunters train young foxes they have caught.