f(x)=4cosxsin(x+π/6)-1
=4cosx(√3/2sinx+1/2cosx)-1
=2√3sinxcosx+2cos^2 x-1
=√3sin2x+cos2x
=2sin(2x+π/6)
从而 f(x)的最小正周期T=2π/2=π