问题
填空题
设向量
|
答案
根据题意,由
=(2,1),a
+3a
=(5,4),b
可得,
=b
[(1 3
+3a
)-b
]=(1,1),a
则|
|=a
,|5
|=b
,2
cosθ=
=2×1+1×1
×2 5
,3 10
则sinθ=
=1-cos2θ
.10 10
设向量
|
根据题意,由
=(2,1),a
+3a
=(5,4),b
可得,
=b
[(1 3
+3a
)-b
]=(1,1),a
则|
|=a
,|5
|=b
,2
cosθ=
=2×1+1×1
×2 5
,3 10
则sinθ=
=1-cos2θ
.10 10