正弦函数周期最小2π,sin(x+2π）=sinx
2x最小正周期2π,T=2π/2=π
f(x)最小正周期为π
sinx单调增区间2kπ-π/2到2kπ+π/2
2x－π/6属于2kπ-π/2到2kπ+π/2
解得x∈﹙-π/6＋kπ,π／3＋kπ﹚