问题 解答题

已知等差数列{an}满足:a3=6,a2+a5=14,{an}的前n项的各为Sn.求an及Sn

答案

设等差数列{an}的公差为d,则

a3=a1+2d=6
a2+a5=2a1+5d=14

解之可得a1=d=2 …(5分)

所以an=2+2(n-2)=2n…(7分)

代入求和公式可得Sn=na1+

n(n-1)
2
d=2n+n(n-1)=n2+n…(12分)

排序题

选择下列每组句子的对话顺序。

1. (1). Hi, Kate. Next Sunday is my birthday. Can you come to my birthday party?

    (2). OK. I'm sure he would love to come.

    (3). Hi, Ann!

    (4). Five. Don't forget to tell Jim. I hope he can come, too.

    (5). Oh, thanks very much. I'd love to. What time is it going to start?

A. (1)-(5)-(4)-(3)-(2)

B. (3)-(2)-(5)-(4)-(1)

C. (1)-(3)-(5)-(4)-(2)

D. (3)-(1)-(5)-(4)-(2)

2. (1). May I speak to Rose?

    (2). Certainly.

    (3). Will you take a message?

    (4). Sorry, she is not in at the moment.

    (5). Please tell her to return me the dictionary tomorrow.

A. (1)-(4)-(3)-(2)-(5)

B. (1)-(2)-(3)-(4)-(5)

C. (1)-(2)-(3)-(5)-(4)

D. (1)-(4)-(2)-(5)-(3)

3. (1). Yes, it's very nice. What's the time?

    (2). It's four o'clock.

    (3). I have a new watch. Do you like it?

    (4). Let's go!

    (5). Oh, it's time to play games!

(A). 3-1-2-5-4

(B). 1-3-5-4-2

(C). 5-2-4-3-1

(D). 2-3-1-5-4

4. (1). Are you sure?

   (2). Can you mend it?

   (3). If he can't, nobody can.

   (4). Something is wrong with my TV set.

   (5). Sorry. But Uncle Wang can.

   (6). Let me see. Oh, it's broken.

A. (6)-(4)-(1)-(2)-(5)-(3)

B. (2)-(4)-(1)-(6)-(3)-(5)

C. (4)-(6)-(2)-(5)-(1)-(3)

D. (4)-(2)-(1)-(3)-(6)-(5)

5. (1). Black and white.

    (2). Will you show me a jacket?

    (3). OK. I will take one.

    (4). I think you look nice in yellow, and it is popular.

    (5). Certainly. What colour would you like?

A. (5)-(1)-(4)-(3)-(2)

B. (2)-(5)-(1)-(4)-(3) 

C. (3)-(5)-(4)-(2)-(1)

D. (5)-(4)-(1)-(2)-(3)

单项选择题