摘要：4．计算:2, (2)(-2a-)2．
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计算：①
+
=
，②
-
=
，③（-
）2=
，④
-
=
，⑤
+
=
=
；
，⑦
-
=
+
=
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| 2 |
| a |
| 3 |
| a |
| 5 |
| a |
| 5 |
| a |
| b |
| a |
| c |
| b |
| b2-ac |
| ab |
| b2-ac |
| ab |
| 3b |
| 2a |
| 9b2 |
| 4a2 |
| 9b2 |
| 4a2 |
| 1 |
| x |
| 1 |
| y |
| y-x |
| xy |
| y-x |
| xy |
| 2a |
| a-b |
| a+b |
| b-a |
1
1
⑥| x2-1 |
| (x+1)2 |
| () |
| x+1 |
| x-1 |
| x+1 |
| x-1 |
| x+1 |
| a2 |
| a+3 |
| 9 |
| a+3 |
a-3
a-3
；⑧| a |
| a-b |
| b |
| b-a |
1
1
．