f(x)=sinx 乘cosx-根号3乘cosx的平方+2分之√3

1个回答

  • f(x)=sinxcosx-√3cos²x+√3/2

    =sin(2x)/2-√3[cos(2x)+1]/2+√3/2

    =(1/2)sin(2x)-(√3/2)cos(2x)

    =sin(2x)cos(π/3)-cos(2x)sin(π/3)

    =sin(2x-π/3)

    最小正周期Tmin=2π/2=π

    当2kπ-π/2≤2x-π/3≤2kπ+π/2 (k∈Z)时,sin(2x-π/3)单调递增,

    此时x∈[kπ-π/12,kπ+5π/12] (k∈Z)

    当2kπ+π/2≤2x-π/3≤2kπ+3π/2 (k∈Z)时,sin(2x-π/3)单调递减,

    此时x∈[kπ+5π/12,kπ+11π/12] (k∈Z)

    函数f(x)的单调递增区间为∈[kπ-π/12,kπ+5π/12] (k∈Z);

    单调递减区间为[kπ+5π/12,kπ+11π/12] (k∈Z).