cos(2x-x/3)≥√3/2
设：(2x-x/3)=U
2kπ-π/6≤U≤2kπ+π/6
2kπ-π/6≤x(5/3)≤2kπ+π/6
3/5(2kπ-π/6)≤x≤3/5(2kπ+π/6) ,K∈Z