题目内容
若等边△ABC的边长为2，平面内一点M满足
=
+
，则
•
=（ ）
| CM |
| 1 |
| 3 |
| CB |
| 1 |
| 2 |
| CA |
| MA |
| MB |
A．
| B．
| C．-
| D．-
|
由题意可得，
•
=|
||
|COS60°=2×2×
=2，
2=
2=4
∵
=
+
∴
=
-
=
-(
+
)=
-
=
-
=
-(
+
)=
-
∴
•
=(
-
)•(
-
)
=
•
-
2-
2
=
×2-
×4-
×4=-
故选C
| CA |
| CB |
| CA |
| CB |
| 1 |
| 2 |
| CA |
| CB |
∵
| CM |
| 1 |
| 3 |
| CB |
| 1 |
| 2 |
| CA |
∴
| MA |
| CA |
| CM |
| CA |
| 1 |
| 3 |
| CB |
| 1 |
| 2 |
| CA |
| 1 |
| 2 |
| CA |
| 1 |
| 3 |
| CB |
| MB |
| CB |
| CM |
| CB |
| 1 |
| 3 |
| CB |
| 1 |
| 2 |
| CA |
| 2 |
| 3 |
| CB |
| 1 |
| 2 |
| CA |
∴
| MA |
| MB |
| 1 |
| 2 |
| CA |
| 1 |
| 3 |
| CB |
| 2 |
| 3 |
| CB |
| 1 |
| 2 |
| CA |
=
| 1 |
| 2 |
| CA |
| CB |
| 1 |
| 4 |
| CA |
| 2 |
| 9 |
| CB |
=
| 1 |
| 2 |
| 1 |
| 4 |
| 2 |
| 9 |
| 8 |
| 9 |
故选C
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相关题目
，平面内一点M满足
＝
＋
，则
·
＝______________.