qben2
幼苗
共回答了25个问题采纳率:96% 举报
(1)f(x)=2
3 sin
x
2 cos
x
2 +2cos 2
x
2 -1=
3 sinx+cosx=2sin(x+
π
6 ),
∵ω=1,
∴f(x)的最小正周期T=2π;
(2)∵f(α)=2sin(α+
π
6 )=2,
即sin(α+
π
6 )=1,
∵
π
6 <α+
π
6 <
2π
3 ,
∴α+
π
6 =
π
2 ,
即α=
π
3 ,
∵f(β)=2sin(β+
π
6 )=
8
5 ,
即sin(β+
π
6 )=
4
5 <
3
2 ,
∴
π
6 <β+
π
6 <
π
2 ,cos(β+
π
6 )=
3
5 ,
则f(α+β)=2sin(α+β+
π
6 )=2sin(
π
2 +β)=2cosβ=2cos[(β+
π
6 )-
π
6 ]=2cos(β+
π
6 )cos
π
6 +2sin(β+
π
6 )sin
π
6 =
3
3 +4
5 .
1年前
3