cos(π/6-2α)=cos(π/6)*cos2α-sin(π/6)*sin2α=(√3cos2α+sin2α)/2=[√3(cos²α-sin²α)+2cosα*sinα]/2 (上下同除cos²α)=[√3(1-tan²α)+2tanα]/2=.自己算tan(α+π/6)=sin(α+π/6)/...