f(x)=sin2/3x+cos(2/3x-丌/6)
=sin2/3x+√3/2*cos2/3x+1/2*sin2/3x
=3/2sin2/3x+√3/2*cos2/3x
=√3sin(2x/3+π/6)
T=3π
任意实数a.b,f(a)-f(b)最大时
|a-b|的最小值是T/2=3π/2