运用了和差角公式cos[(x+π/3)-π/3]=cos[(x+π/3)-π/3]=cosx+π/3cosπ/3+sinx+π/3sinπ/3=cosx+π/31/2+sinx+π/3√3/2sin(α±β)=sinαcosβ±cosαsinβcos(α-+β)=cosαcosβ±sinαsinβ
