题目内容
计算．
（1）a+b+
；
（2）(x+1-
)÷
；
（3）(2+
-
)÷(a-
)，其中a=2．
（1）a+b+
| 2b2 |
| a-b |
（2）(x+1-
| 3 |
| x-1 |
| x+2 |
| 2x-2 |
（3）(2+
| 1 |
| a-1 |
| 1 |
| a+1 |
| a |
| 1-a2 |
（1）a+b+
=
+
=
；
（2）(x+1-
)÷
=[
-
]×
=
×
=2x-4；
（3）(2+
-
)÷(a-
)，
=[
+
-
]÷[
+
]
=
×
=
，
把a=2代入原式得：原式=
=1．
| 2b2 |
| a-b |
=
| (a+b)(a-b) |
| a-b |
| 2b2 |
| a-b |
=
| a2+b2 |
| a-b |
（2）(x+1-
| 3 |
| x-1 |
| x+2 |
| 2x-2 |
=[
| (x+1)(x-1) |
| x-1 |
| 3 |
| x-1 |
| 2(x-1) |
| x+2 |
=
| (x+2)(x-2) |
| x-1 |
| 2(x-1) |
| x+2 |
=2x-4；
（3）(2+
| 1 |
| a-1 |
| 1 |
| a+1 |
| a |
| 1-a2 |
=[
| 2(a+1)(a-1) |
| (a+1)(a-1) |
| (a+1) |
| (a-1)(a+1) |
| a-1 |
| (a+1)(a-1) |
| a(a+1)(a-1) |
| (a+1)(a-1) |
| a |
| (a+1)(a-1) |
=
| 2a2 |
| (a+1)(a-1) |
| (a+1)(a-1) |
| a3 |
=
| 2 |
| a |
把a=2代入原式得：原式=
| 2 |
| a |
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