问题
选择题
平面上O，A，B三点不共线，设
|
答案
S△OAB=
|1 2
||a
|sin＜b
，a
＞b
=
|1 2
||a
|b 1-cos2＜
，a
＞b
=
|1 2
||a
|•b 1- (
•a
)2b |
|2|a
|2b
=1 2
；|
|2|a
|2-(b
•a
)2b
故选C．
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平面上O，A，B三点不共线，设
|
S△OAB=
|1 2
||a
|sin＜b
，a
＞b
=
|1 2
||a
|b 1-cos2＜
，a
＞b
=
|1 2
||a
|•b 1- (
•a
)2b |
|2|a
|2b
=1 2
；|
|2|a
|2-(b
•a
)2b
故选C．
| 句型转换填空。 |
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