问题
填空题
已知|
|
答案
设
与a
的夹角为θ则b
∵
•(a
-b
)=2a
即
•a
-b
2= 2a
∵|
|=1，a
•a
-1 = 2b
∴
•a
=3b
∴cosθ=
=
•a b |
||a
|b
=3 6 1 2
∵θ∈[0，π]
∴θ=π 3
故答案为：π 3
搜题请搜索小程序“爱下问搜题”
已知|
|
设
与a
的夹角为θ则b
∵
•(a
-b
)=2a
即
•a
-b
2= 2a
∵|
|=1，a
•a
-1 = 2b
∴
•a
=3b
∴cosθ=
=
•a b |
||a
|b
=3 6 1 2
∵θ∈[0，π]
∴θ=π 3
故答案为：π 3