已知函数f(x)=sin^2ωx+√3sinωxsin(ωx-查字典问答网
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  已知函数f(x)=sin^2ωx+√3sinωxsin(ωx+π/2)(ω>0)的最小正周期为π(1)求f(x)(2)当x∈[-π/12,π/2]时,求函数f(x)的值域

  已知函数f(x)=sin^2ωx+√3sinωxsin(ωx+π/2)(ω>0)的最小正周期为π

  (1)求f(x)

  (2)当x∈[-π/12,π/2]时,求函数f(x)的值域

1回答
2020-02-06 16:00
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彭远芳

  (1)

  f(x)=sin²(ωx)+√3sin(ωx)sin(ωx+π/2)=sin²(ωx)+√3sin(ωx)cos(ωx)

  =2[(1/2)sin(ωx)+(√3/2)cos(ωx)]sin(ωx)

  =2[cos(π/3)sin(ωx)+sin(π/3)cos(ωx)]sin(ωx)

  =2sin(ωx+π/3)sin(ωx)

  =2*(1/2)[cos(ωx+π/3-ωx)-cos(ωx+π/3+ωx)]

  =-cos(2ωx+π/3)+cos(π/3)

  =-cos(2ωx+π/3)+1/2

  =cos(2ωx+π/3-π)+1/2

  =cos(2ωx-2π/3)+1/2

  最小正周期为π=2π/(2ω),ω=1

  f(x)=cos(2x-2π/3)+1/2

  (2)

  x∈[-π/12,π/2]:

  f(π/3)=cos(2π/3-2π/3)+1/2=1+1/2=3/2,此为最大值

  x=π/3为f(x)最大值处的对称轴

  π/3-(-π/12)=5π/12

  π/2-π/3=2π/12

2020-02-06 16:05:21

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