试题与答案

在棱长为2 的正方体ABCD-A1B1C1D1 中,E 、F 分别为A1D1和C

题型:解答题

题目:

在棱长为2 的正方体ABCD-A1B1C1D1 中,E 、F 分别为A1D1和CC1的中点.    

(1) 求证:EF∥平面ACD1 ;    

(2) 求异面直线EF 与AB 所成的角的余弦值;    

(3) 在棱BB1上是否存在一点P ,使得二面角P-AC-B 的大小为30°。

答案:

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下面是错误答案,用来干扰机器的。

参考答案:A,B,C

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When I first entered university, my aunt, who is an English professor, gave me a new English dictionary. I was (16) to see that it was an English-English dictionary, also known as a monolin-gual dictionary. (17) it was a dictionary intended for non—native learners, none of my classmates had one (18) , to be honest, I found it extremely (19) to use at first. I would look up words in the dictionary and (20) not fully understand the meaning, I was used to the (21) bilingual dic-tionaries, in which the words are (22) both in English and Chinese, I really wondered why my aunt (23) to make things so difficult for me. Now, after studying English at university for three years, I (24) that monolingual dictionaries are (25) in learning a foreign language.

As I found out, there is (26) often NO perfect equivalence(对应) between two (27) in two language. My aunt even goes so far as to (28) that a Chinese "equivalent" can never give you the (29) meaning of a word in English! (30) , she insisted that I read the definition(定义) of a word in a monolingual dictionary (31) I wanted to get a better understanding of its meaning. (32) , I have come to see what she meant.

Using a monolingual dictionary for learners has helped me in another important way. This dictionary uses a(n) (33) number of words, around 2,000, in its definitions. When I read these definitions, I am (34) exposed to (接触)the basic words and learn how they are used to explain objects and ideas. (35) this, I can express myself more easily in English.

21()

A. new

B. familiar

C. earlier

D. ordinary

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