题目

(本题满分12分) 设．数列满足 ．（1）求证：是等差数列； （2）求证：  答案：略 解析:（1）由，令，得 ，（） 两式相减，得＝且时也成立． 所以，即是等差数列． （2）设， 而，又 所以．I knew little about English when I first came to America．So I went to a language school every day to   1   English．One day，during the break，I asked one of my classmates a question．When I tanked her for it，she said，"   2  ．It's a piece of cake．"I thought to  3   ，"She wants a piece of cake? "So I said to her，"I haven't taken any piece of 4  with me today．What about a piece of biscuit（'饼干） ?" She looked at me in surprise and then smiled．She knew that I didn't   5  her．She said，"What I mean is no problem．"Then I began to learn that" a piece of cake" is not only a piece of cake，but also means a thing that is very easy． 1．A．tell                  B．know             C．teach              D．learn 2．A．All right                                           B．The same to you  C．You're welcome                                       D．Nothing serious 3．A．yourself              B．myself           C．himself            D．herself 4．A．bread               B．pizza              C．biscuit           D．cake 5．A．understand          B．remember        C．find               D．believe