已知函数(x)=sinx ^2+sinxcos求其最小正周期

1个回答

  • ∵cos2χ=1-2sin²x

    ∴sin²x=½﹙1-cos2χ﹚

    又sinxcosx=½sin2x

    f(x)=sinx ^2+sinxcosx

    =½﹙1-cos2χ﹚ +½sin2x

    =½sin2x-½cos2χ+½

    =√2/2sin﹙2x-π/4﹚+½

    ∴其最小正周期2π/2=π

    ∵0≤x≤π/2

    ∴-π/4≦2x-π/4≦3π/4

    -1/√2≦2sin﹙2x-π/4﹚≦1

    ∴0≦√2/2sin﹙2x-π/4﹚+½≦√2/2+½

    ∴f﹙x﹚的最大值为√2/2+½

    2x-π/4=π/2 x=3π/8

    f﹙x﹚的最小值为0

    ∴-π/4=2x-π/4

    x=0