f（x）=3sin（2x-π/3）
T=2π/2=π
振幅:3
初相-π/3
2x-π/3在[2kπ-π/2,2kπ+π/2]单调递增
x在[kπ-5π/12,kπ+π/12]单调递增
2x-π/3在[kπ+π/2,2kπ+3π/2]单调递减
x在[kπ+π/12,2kπ+7π/12]单调递减