函数为y=2sin(3x+π/3)
对称轴 3x+π/3=2kπ+π/2
化简得x=2kπ/3+π/18 k为整数
单调增区间 2kπ-π/2≤3x+π/3≤2kπ+π/2 化简可得
减区间同理 2kπ+π/2≤3x+π/3≤2kπ+3π/2