题目内容
先化简,再求值:
(1)
+
,其中a=
.
(2)
+
-
,其中a=-2,b=
.
(1)
2a |
a2-4 |
1 |
2-a |
1 |
2 |
(2)
a+2b |
a+b |
2b2 |
a2-b2 |
2ab |
a2-b2 |
1 |
3 |
(1)原式=
-
=
=
=
,
当a=
时,原式=
=
;
(2)原式=
+
-
=
=
=
=
,
当a=-2,b=
时,原式=
=
.
2a |
(a+2)(a-2) |
a+2 |
(a+2)(a-2) |
=
2a-a-2 |
(a+2)(a-2) |
=
a-2 |
(a+2)(a-2) |
=
1 |
a+2 |
当a=
1 |
2 |
1 | ||
|
2 |
5 |
(2)原式=
(a+2b)(a-b) |
(a+b)(a-b) |
2b2 |
(a+b)(a-b) |
2ab |
(a+b)(a-b) |
=
a2+ab-2b2+2b2-2ab |
(a+b)(a-b) |
=
a2-ab |
(a+b)(a-b) |
=
a(a-b) |
(a+b)(a-b) |
=
a |
a+b |
当a=-2,b=
1 |
3 |
-2 | ||
-2+
|
6 |
5 |
练习册系列答案
相关题目