y=2sin(1/2x+pai/3)
周期2π/(1/2)=4π
最大值2,最小值-2
单增区间
2kπ-π/2≤1/2x+π/3≤2kπ+π/2
2kπ-5π/6≤1/2x≤2kπ+π/6
4kπ-5π/3≤x≤4kπ+π/3
单减区间
4kπ+π/3≤x≤4kπ+7π/3