题目内容
已知向量
,
的夹角为60°,且|
|=2,|
|=1,若
=
-4
,
=
+2
,求
(1)
•
;
(2)|
+
|.
a |
b |
a |
b |
c |
a |
b |
d |
a |
b |
(1)
a |
b |
(2)|
c |
d |
(1)
•
=|
|×|
|cos60°=2×1×
=1;
(2)∵
+
=2
-2
,∴|
+
|=
=
=2
=2
=2
.
a |
b |
a |
b |
1 |
2 |
(2)∵
c |
d |
a |
b |
c |
d |
(
|
(2
|
|
22-2×1+12 |
3 |
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