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  • 已知函數(shù)f(x)=sin(2x+π/3)+sin(2x-π/3)+2cos^2x-1

    已知函數(shù)f(x)=sin(2x+π/3)+sin(2x-π/3)+2cos^2x-1
    (1)求函數(shù)的最小正周期 (2)求f(x)在區(qū)間{-π/4,π/4}上的最大值和最小值,
    其他人氣:954 ℃時間:2019-11-06 19:12:12
    優(yōu)質(zhì)解答
    f(x)=sin(2x+π/3)+sin(2x-π/3)+2cos^2x-1
    =sin2xcosπ/3+cos2xsinπ/3+sin2xcosπ/3-cos2xsinπ/3+cos2x
    =2sin2xcosπ/3+cos2x
    =sin2x+cos2x
    =√2*(√2/2*sin2x+√2/2*cos2x)
    =√2*(sin2xcosπ/4+cos2xsinπ/4)
    =√2*sin(2x+π/4)
    T=2π/2=π
    x∈[-π/4,π/4]
    2x∈[-π/2,π/2]
    2x+π/4∈[-π/4,3π/4]
    -1<=√2*sin(2x+π/4)<=√2
    f(x)在區(qū)間[-π/4,π/4]上的最大值為:√2
    f(x)在區(qū)間[-π/4,π/4]上的最小值為:-1
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