f(x)=sin(1/2x+π/3)+cos(1/2x-π/6)=sin(1/2x+π/3)+sin(1/2x-π/6+π/2)(诱导公式）=2sin(1/2x+π/3)
再y=Asin(wx+fai)中最小正周期T=2π/|w|,所以T=2π/(1/2)=4π