sinx>0.5 ==> x1∈[π/6+2kπ,5π/6+2kπ]
cosx>-0.5 ==> x2∈[-2π/3+2kπ,2π/3+2kπ]
x1∩x2是 [π/6+2kπ,2π/3+2kπ] k∈Z*