问题 填空题

给出下列命题:

①命题“∃x∈R,x2-x>0”的否定是“∀x∈R,x2-x≤0”;

②命题“若am2<bm2,则a<b”的逆命题是真命题;

③f(x)是(-∞,0)∪(0,+∞)上的奇函数,x>0时的解析式是f(x)=2*.则x<0时的解析式为f(x)=-2-x

④若随机变量ξ~N(1,σ2),且P(0≤ξ≤1)=0.3,则P(ξ≥2)=0.2.

其中真命题的序号是______.(写出所有你认为正确命题的序号)

答案

对于①,它是一个含有量词的命题,“∃x∈R,x2-x>0”即“存在x∈R,使得x2-x>0成立”,其否定应该是不存在满足条件的x,也就是说,对于任意的x∈R,都有x2-x≤0,即“∀x∈R,x2-x≤0”,故①正确;

对于②,“若am2<bm2,则a<b”的逆命题为“若a<b,则am2<bm2,当m=0时不成立,故为假命题,即②不正确;

对于③,设x<0,则-x>0,∴f(-x)=2-x,∵函数是(-∞,0)∪(0,+∞)上的奇函数,∴f(x)=-f(x)=-2-x,即③正确;

对于④若随机变量ξ~N(1,σ2),且P(0≤ξ≤1)=0.3,则P(ξ≥2)=P(ξ≤0)=1-0.3=0.2,即④正确.

故答案为:①③④.

阅读理解

Mr. and Mrs. Harris had always spent their summer holidays in a small hotel at the seaside near their hometown. One year, however, Mr.  Harris made a lot of money in his factory, so they decided to go to a foreign country and stay at a really good hotel.

They flew to Paris, and arrived at a 5-star hotel late in the evening. They thought they would have to go to bed hungry, because in that small hotel where they used to stay in the past, no meals were served after seven in the evening. They were surprised to be told that the hotel served dinner until ten.

"Then what are the times of meals?" asked Mrs. Harris.

"Well, Madam, we serve breakfast from seven to eleven, lunch from twelve to three, tea from four to five, and dinner from six to ten."

"But that hardly leaves any time for us to see the city!" said Mrs. Harris.

小题1:Why did Mr. and Mrs. Harris think they would have to go to bed hungry when they arrived at the hotel?

A.Because it’s a 5-star hotel.

B.Because they thought no meals would be served late in the evening.

C.Because they were very tired after the trip.

D.Because they didn’t want to eat anything.小题2: How long did the service time for lunch last in the hotel?

A.2 hours.

B.4 hours.

C.3 hours .

D.1 hour.小题3: What did Mrs. Harris think of the times of the meals in the hotel?

A.She thought they would have enough time to see the city.

B.She thought they would have to spend too much time on meals instead of travelling.

C.She thought they would have enough time to have meals.

D.She thought the times were suitable and felt very satisfied.

单项选择题 A1型题