观察下列各式:1×12=1-12;12×3=12-13;13×4=13-14;…

题型:解答题

问题:

观察下列各式:
1
2
=1-
1
2
1
2×3
=
1
2
-
1
3
1
3×4
=
1
3
-
1
4
;…
(1)猜想它的规律,把
1
n×(n+1)
(n为正整数)表示出来.
(2)用你得到的规律,计算:
1
2
+
1
6
+
1
12
+…+
1
n(n+1)
,并求出当n=24时代数式的值.
考点:分式的加减
题型:解答题

阅读理解。

       I'm Tom. Look! This is a pencil case. It's orange. It's my pencil case. What's in the pencil case?

There is a ruler, a pencil and an eraser in it. This is my ruler. It is blue and red. This is a pencil. It is

black and white. Oh, it is not my pencil. I think it's Lucy's pencil. And the big and pink eraser is Tony's.

      That boy is Tim. I found his green pen in the lost and found case. I will call him at 7890003. It is

his telephone number.

1. The pencil case is ______?

A. It's golden.

B. It's blue and red.

C. It's green.

D. It's orange.

2. The ______ is Lucy's.

A. pencil

B. ruler

C. pen

D. eraser

3. The eraser is ______.

A. red

B. big

C. purple

D. new

4. ______ found the pen in the lost and found case.

A. Tom

B. Lucy

C. Tim

D. The teacher

5. ______ telephone number is 7890003.

A. Tom's.

B. Lucy's.

C. Tim's.

D. Tony's.

题型:解答题

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A.Ag+、K+、NO3-、HCO3-

B.K+、NH4+、NO3-、SO42-

C.Ag+、NH4+、Mg2+、HCO3-

D.K+、Mg2+、SO42-、Cl-

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实验目的方案1   方案2  
A.清洗铁制品表面的铁锈用适量稀盐酸洗用适量稀硫酸洗
B.鉴别NaOH和Na2CO3固体滴加氢氧化钙溶液滴加无色酚酞溶液
C.干燥二氧化碳将气体通过固体CaO将气体通过浓硫酸
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某公司为满足某种产品的市场需求,拟提出新建、扩建、改建三个方案。方案中销路好的概率为0.3,销路一般的概率为0.5,销路差的概率为0.2。不同销路的损益值见表7-1。预计项目经营期为8年。那么该公司所作的决策是______。 表7-1 展销会各种收益和会场租赁费用表 方案 好(P1=0.3)一般(P2=0.5)差(P3=0.2)需要投资(万元)新建502510160扩建40208110改建2512560

A.选择新建方案
B.选择扩建方案
C.选择改建方案
D.条件不足,难以选择

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如发生青霉素过敏性休克,抢救应首选()

A.肾上腺素

B.去甲肾上腺素

C.抗组胺药

D.多巴胺

E.头孢氨苄

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