问题
解答题
已知|
(1)
(2)(3
|
答案
(1)∵|
|=10,|a
|=12,b
与a
的夹角为120°b
∴
•a
=|b
||a
|cos120°=-60、b
(2)(3
-2b
)•(4a
+a
)=-8|b
|2+10a
•a
+3|b
|2=-968b
已知|
(1)
(2)(3
|
(1)∵|
|=10,|a
|=12,b
与a
的夹角为120°b
∴
•a
=|b
||a
|cos120°=-60、b
(2)(3
-2b
)•(4a
+a
)=-8|b
|2+10a
•a
+3|b
|2=-968b