问题
解答题
(1)已知平面向量
(2)已知|
|
答案
(1)若
⊥a
,则 b
•a
=2x+3-x2=0,∴x=3,或 x=-1.b
(2)已知|
|=3,|a
|=2,b
,a
所成角为60°,∴b
•a
=3×2cos60°=3.b
|2
+a
|=b
=(2
+a
)2b
=4
2+4 a
•a
+b
2b
=36 +12+4
=252
.13
(1)已知平面向量
(2)已知|
|
(1)若
⊥a
,则 b
•a
=2x+3-x2=0,∴x=3,或 x=-1.b
(2)已知|
|=3,|a
|=2,b
,a
所成角为60°,∴b
•a
=3×2cos60°=3.b
|2
+a
|=b
=(2
+a
)2b
=4
2+4 a
•a
+b
2b
=36 +12+4
=252
.13