问题 填空题
(理科)对于函数f(x)=sinx,g(x)=cosx,h(x)=x+
π
3
,有如下四个命题:
(1)f(x)-g(x)的最大值为
2

(2)f[h(x)]在区间[-
π
2
,0]上是增函数;
(3)将f(x)的图象向右平移
π
2
个单位可得g(x)的图象.
(4)g[f(x)]是最小正周期为2π的周期函数.
其中真命题的序号是______.
答案

由于f(x)-g(x)=sinx-cosx=

2
sin(x-
π
4
),故它的最大值等于
2
,故(1)正确.

由于f[h(x)]=sin[(h(x)]=sin(x+

π
3
),当 x∈[-
π
2
,0]时,(x+
π
3
)∈[-
π
6
π
3
]⊂[-
π
2
π
2
],故f[h(x)]在区间[-
π
2
,0]上是增函数,故(2)正确.

将f(x)的图象向右平移

π
2
个单位后得到函数y=sin(x-
π
2
)=cosx=g(x)的图象,故(3)正确.

g[f(x)]=cos(f(x))=cos(sinx),它的最小正周期就是sinx的最小正周期为2π,故(4)正确.

故答案为:(1)、(2)、(3)、(4).

单项选择题 配伍题
单项选择题

When Dave was eighteen, he bought a secondhand car for 200 so that he could travel to and from work more (1) than by bus. It worked quite well for a few years, but then it got so old, and it was costing him (2) much in repairs that he decided that he had better (3) it.

He asked among his friends to see if anyone was particularly (4) to buy a cheap car, but they all knew that it was falling to pieces, so (5) of them had any desire to buy it. Dave’s friend Sam saw that he was (6) when they met one evening, and said, "What’s (7) , Dave"

Dave told him, and Sam answered, "Well, what about advertising it in the paper You may (8) more for it that way than the cost of the advertisement!" Thinking that Sam’s (9) was sensible, he put an advertisement in an evening paper, which read "For sale: small car, (10) very little petrol, only two owners. Bargain at 50. " For two days after the advertisement first appeared, there was no (11) . But then on Saturday evening he had an enquiry. A man rang up and said he would like to (12) him about the car. "All right, " Dave said, feeling happy. He asked the man whether ten o’clock the next morning would be (13) or not. "Fine, " the man said, "and I’ll (14) my wife. We intend to go for a ride in it to (15) it. "

The next morning, at a quarter to ten, Dave parked the car in the square outside his front door, (16) to wait there for the people who had (17) his advertisement. Even Dave had to (18) that the car really looked like a wreck. Then, soon after he had got the car as clean (19) it could be, a police car stopped just behind him and a policeman got out. He looked at Dave’s car and then said, "Have you reported this (20) to us yet, sir\

14().

A.follow 

B.meet 

C.bring 

D.introduce