阅读理11×2=11-12，12×3=12-13…1x(x+1)=1x-1x+1_爱下问搜题

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问题解答题

阅读理

1

1×2

=

1

1

-

1

2

，

1

2×3

=

1

2

-

1

3

…

1

x(x+1)

=

1

x

-

1

x+1

阅读以上信息，完成下列各题：
（1）

1

1×2

+

1

2×3

+

1

3×4

=______；（填最后结果）
（2）

1

x(x+1)

+

1

(x+1)(x+2)

=______；（填最后结果）
（3）求

1

1×2

+

1

2×3

+…+

1

x(x+1)

的值．

答案

∵

1

1×2

=

1

1

-

1

2

，

1

2×3

=

1

2

-

1

3

…

1

x(x+1)

=

1

x

-

1

x+1

，

∴（1）原式=1-

1

2

+

1

2

-

1

3

+

1

3

-

1

4

=1-

1

4

=

3

4

；

（2）原式=

1

x

-

1

x+1

+

1

x+1

-

1

x+2

=

1

x

-

1

x+2

=

2

x(x+2)

；

（3）原式=1-

1

2

+

1

2

-

1

3

+…+

1

x

-

1

x+1

=1-

1

x+1

=

x

x+1

．

故答案为：

3

4

，

2

x(x+2)

．

单项选择题

竹子的分枝方式为（）。

A．单轴分枝

B．合轴分枝

C．二叉分枝

D．分蘖

改错题

Dear sir,

Last year I buy a refrigerator in your store on Chang An road. We all like shape of the refrigerator. And recently I find something is wrong with it. It begins to make noise when it turned on. At first it is low but gradually it become louder and louder. To make the matter worse, it even stops working sometimes. We all feel disappointing. I am writing you to ask for help. Would you please send a people to repair it? I will at home this weekend. Please call me before you come to here. My telephone number is 6606.5531. Thanks you very much.

Customer

Li Ming