y=sin(2/3x)＋(√3/2)cos(2/3x)－(1/2)sin(2/3x)=(1/2)sin(2/3x)＋(√3/2)cos(2/3x)=sin(2/3x＋π/3).两相邻对称轴之间的距离就是半个周期,T/2=(π)/(2/3)=3π/2