已知函数f(x)=sin(2x+π6)+sin(2x−π6)+2cos2x.
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已知函数f(x)=sin(2x+
)+sin(2x−
)+2cos
π |
6 |
π |
6 |
(1)∵f(x)=sin(2x+
π
6)+sin(2x−
π
6)+2cos2x
=sin2xcos
π
6+cos2xsin
π
6+sin2xcos
π
6−cos2xsin
π
6+2cos2x+1
=
3sin2x+cos2x+1
=2sin(2x+
π
6)+1.
∴f(x)max=2+1=3.T=
2π
|ω|=
2π
2=π.
(2)∵f(x)≥2,∴2sin(2x+
π
6)+1≥2.
∴sin(2x+
π
6)≥
1
2.
∴2kπ+
π
6≤2x+
π
6≤2kπ+
5
6π,
∴kπ≤x≤kπ+
π
3(k∈Z),
∴f(x)≥2的x的取值范围是{x|kπ≤x≤kπ+
π
3,k∈Z}.
π
6)+sin(2x−
π
6)+2cos2x
=sin2xcos
π
6+cos2xsin
π
6+sin2xcos
π
6−cos2xsin
π
6+2cos2x+1
=
3sin2x+cos2x+1
=2sin(2x+
π
6)+1.
∴f(x)max=2+1=3.T=
2π
|ω|=
2π
2=π.
(2)∵f(x)≥2,∴2sin(2x+
π
6)+1≥2.
∴sin(2x+
π
6)≥
1
2.
∴2kπ+
π
6≤2x+
π
6≤2kπ+
5
6π,
∴kπ≤x≤kπ+
π
3(k∈Z),
∴f(x)≥2的x的取值范围是{x|kπ≤x≤kπ+
π
3,k∈Z}.
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