sin(30°-a)-sin(60°-a)=?
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)=
=cos(a)+sqrt(3)*cos(a)