已知向量
(Ⅰ)求函数f(x)的最小正周期; (Ⅱ)在△ABC中,若f(A)=4,b=1,△ABC的面积为
|
(Ⅰ)∵向量
=(m
sin2x+2,cosx),3
=(1,2cosx),n
∴函数f(x)=
•m
=n
sin2x+2+2cos2x3
=
sin2x+cos2x+33
=2sin(2x+
)+3.π 6
∴T=
=π.2π 2
(Ⅱ)由f(A)=4得,2sin(2A+
)+3=4,∴sin(2A+π 6
)=π 6
.1 2
又∵A为△ABC的内角,∴
<2A+π 6
<π 6
,∴2A+13π 6
=π 6
,解得A=5π 6
.π 3
∵
bcsinA=1 2
,b=1,3 2
∴
×1×csin1 2
=π 3
,解得c=2.3 2
由余弦定理可得a2=b2+c2-2bccosA=4+1-2×2×1×
=3.1 2
∴a=
.3