题目内容
若等边△ABC的边长为2
，平面内一点M满足
=
+
，则
•
=（ ）
| 3 |
| CM |
| 1 |
| 3 |
| CB |
| 1 |
| 3 |
| CA |
| MA |
| MB |
| A．-2 | B．2 | C．-2
| D．2
|
∵
=
+
∴
=
-
=
-(
+
)=
-
=
-
=
-(
+
) =
-
∴
•
=(
-
) • (
-
)=
•
-
|
|2 -
|
|2=
×|
| ×|
| ×cos60°-
(2
)2-
(2
)2
=
×2
×2
×
-
×12-
×12=
-
=-2
故选A
| CM |
| 1 |
| 3 |
| CB |
| 1 |
| 3 |
| CA |
∴
| MA |
| CA |
| CM |
| CA |
| 1 |
| 3 |
| CB |
| 1 |
| 3 |
| CA |
| 2 |
| 3 |
| CA |
| 1 |
| 3 |
| CB |
| MB |
| CB |
| CM |
| CB |
| 1 |
| 3 |
| CB |
| 1 |
| 3 |
| CA |
| 2 |
| 3 |
| CB |
| 1 |
| 3 |
| CA |
∴
| MA |
| MB |
| 2 |
| 3 |
| CA |
| 1 |
| 3 |
| CB |
| 2 |
| 3 |
| CB |
| 1 |
| 3 |
| CA |
| 5 |
| 9 |
| CA |
| CB |
| 2 |
| 9 |
| CA |
| 2 |
| 9 |
| CB |
| 5 |
| 9 |
| CA |
| CB |
| 2 |
| 9 |
| 3 |
| 2 |
| 9 |
| 3 |
=
| 5 |
| 9 |
| 3 |
| 3 |
| 1 |
| 2 |
| 2 |
| 9 |
| 2 |
| 9 |
| 30 |
| 9 |
| 48 |
| 9 |
故选A
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相关题目
，平面内一点M满足
＝
＋
，则
·
＝______________.