cos（α‐π/6)+sinα=4/5*√3
cosαcos(π/6)+sinαsin(π/6)+sinα=4/5*√3
√3/2*cosα+3/2*sinα=4/5*√3
1/2*cosα+√3/2*sinα=4/5
sin(α+π/6)=4/5
sin(α+7/6π〕=-sin(α+π/6)=-4/5