问题
解答题
已知向量
(Ⅰ)若
(Ⅱ)当k=1时,
(Ⅲ)若|
|
答案
(Ⅰ)∵
⊥a
,∴c
•a
=0,∴c
+3
k=0,解得k=-1;3
(Ⅱ)∵k=1,∴
=(a
,1),又3
=(0,-1),∴b
-λa
=(b
,1-λ).3
∵
-λa
与b
共线,∴c
×3
-(1+λ)=0,解得λ=2;3
(Ⅲ)∵|
|=b
=1,∴|0+(-1)2
|=m
.3
又
与m
的夹角为150°,|c
|=c
=2.1+(
)23
∴
•m
=|c
| |m
|cos150°=c
×2×cos150°=-3,3
|
+2m
|=c
=
2+4m
•m
+4c
2c
=(
)2+4×(-3)+4×223
.7