题目内容
已知
，
都是单位向量，
•
=-
，则|
-
|=______．
| a |
| b |
| a |
| b |
| 1 |
| 2 |
| a |
| b |
|
-
|2=(
-
)2
=
2-2
•
+
2
2-2×( -
)=3，∴|
-
|=
．
故答案为：
| a |
| b |
| a |
| b |
=
| a |
| a |
| b |
| b |
2-2×( -
| 1 |
| 2 |
| a |
| b |
| 3 |
故答案为：
| 3 |
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题目内容
| a |
| b |
| a |
| b |
| 1 |
| 2 |
| a |
| b |
| a |
| b |
| a |
| b |
| a |
| a |
| b |
| b |
| 1 |
| 2 |
| a |
| b |
| 3 |
| 3 |
