（1）f（x）=2sin（x-π/6）cosx+2cos^2x=（√3sinx-cosx）cosx+2cosxcosx
=（√3sinx+cosx）cosx=√3/2sin2x+1/2cos2x+1/2
=sin（2x+π/6）+1/2
令2kπ-π/2