Sin(30+a) - cos (60+a) \ sin(30+a) + cos (60+a) =

Sin(30-a)-cos(60-a)=sin30*cos(a)-sin(a)*cos30-cos60*cos(a)-sin60*sin(a)=cos(a)/2-√3*sin30/2-cos(a)/2-√3*sin(a)/2=-√3sin(a)/.