Sin(30+a) - cos (60+a) \ sin(30+a) + cos (60+a) =
1.sin(30°-a)-sin(60°-a)=sin(30°)cos(a)-cos(30°)sin(a)-(sin(60°)cos(a)-cos(60°)sin(a))=1/2*cos(a)-sqrt(3)/2*sina-sqrt(3)/2*sin(a)+1/2*cos(a)=