问题:
已知向量
a
,
b
满足|
a
|=5,|
b
|=3,|
a
-
b
|=7,则
a
•
b
=______.
已知向量
,
满足|
|=5,|
|=3,|
-
|=7,则
•
=______.
a |
b |
a |
b |
a |
b |
a |
b |
参考答案: