题目内容
如图,已知点O是边长为1的等边△ABC的中心,则(
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A.

B.

C.

D.

【答案】分析:由题意求出
的长度,推出夹角大小,直接利用向量的数量积求解即可.
解答:解:因为点O是边长为1的等边△ABC的中心,D为BC的中点,
两两夹角为120°.
所以
=
=
.
所以(
)•(
)
=
=
+
+
+
=
=-
.
故选D.
点评:本题考查向量的数量积的运算,利用条件求出
的值,已经向量的夹角是解题的关键.

解答:解:因为点O是边长为1的等边△ABC的中心,D为BC的中点,

所以
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

所以(


=

=




=

=-

故选D.
点评:本题考查向量的数量积的运算,利用条件求出


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