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  • 已知函數(shù)f(x)=cos(2x-π/3)+2sin(x-π/4)求函數(shù)在區(qū)間[0,π/2]上的值域

    已知函數(shù)f(x)=cos(2x-π/3)+2sin(x-π/4)求函數(shù)在區(qū)間[0,π/2]上的值域
    求函數(shù)單調(diào)區(qū)間
    打錯(cuò)了...f(x)=cos(2x-π/3)+2sin(x-π/4)sin(x+π/4)
    數(shù)學(xué)人氣:325 ℃時(shí)間:2019-12-20 14:08:51
    優(yōu)質(zhì)解答
    f(x)=cos(2x-π/3)+2sin(x-π/4)sin(x+π/4)=cos(2x-π/3)+2sin(x-π/4)cos[π/2-(x+π/4)]
    =cos(2x-π/3)+2sin(x-π/4)cos(x-π/4)=cos(2x-π/3)+sin(2x-π/2)
    =cos(2x-π/3)+cos2x=2cos(2x-π/6)cosπ/6=√3cos(2x-π/6)
    ∵x∈[0,π/2] ∴2x-π/6∈[﹣π/6,5π/6] ∴f(x)∈[﹣3/2,√3]
    ∴當(dāng)2x-π/6∈[2kπ,2kπ+π] 即x∈[kπ+π/12,kπ+7π/12] 時(shí),單調(diào)遞增
    當(dāng)2x-π/6∈[2kπ+π,2kπ+2π] 即x∈[kπ+7π/12,kπ+13π/12] 時(shí),單調(diào)遞減
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