题目内容
观察下列各式的化简过程:
=
+1①,
=
+
②,
=
+
③,
…
=
+
,
=
+
.
(1)写出①式具体的化简过程.
(2)从上面的式子中,你发现了什么规律?
(3)利用上面的规律,试计算:
-
+
-…+
的值.
1 | ||
|
2 |
1 | ||||
|
3 |
2 |
1 | ||||
|
4 |
3 |
…
1 | ||||
|
2002 |
2001 |
1 | ||||
|
2003 |
2002 |
(1)写出①式具体的化简过程.
(2)从上面的式子中,你发现了什么规律?
(3)利用上面的规律,试计算:
1 | ||
|
1 | ||||
|
1 | ||||
|
1 | ||||
|
分析:(1)把
变成
,求出即可;
(2)
=
+
;
(3)把
-
+
-…+
变成
+1-(
+
)+(
+
)-(
+
)-…+
+
,去括号后合并即可.
1 | ||
|
1×(
| ||||
(
|
(2)
1 | ||||
|
n+1 |
n |
(3)把
1 | ||
|
1 | ||||
|
1 | ||||
|
1 | ||||
|
2 |
3 |
2 |
4 |
3 |
5 |
4 |
400 |
399 |
解答:解:(1)
=
=
=
+1;
(2)
=
+
;
(3)
-
+
-…+
=
+1-(
+
)+(
+
)-(
+
)-…+
+
=1+
=1+20
=21.
1 | ||
|
=
1×(
| ||||
(
|
=
| ||
2-1 |
=
2 |
(2)
1 | ||||
|
n+1 |
n |
(3)
1 | ||
|
1 | ||||
|
1 | ||||
|
1 | ||||
|
=
2 |
3 |
2 |
4 |
3 |
5 |
4 |
400 |
399 |
=1+
400 |
=1+20
=21.
点评:本题考查了分母有理化的应用,关键是能根据题意得出规律.
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