(7) =sin(a+b)cos(b-y)-cos(a+b)sin(b-γ)=sin(a+b-(b-y))=sin(a-y) ;
(8) =sin(a-b)cos(y-b)-cos(a-b)sin(γ-b) =sin(a-b-(y-b))=sin(a-y) ;
(9) =(tanπ/4+tan5π/12) /( 1-tan5π/12)=tan(π/4+5π/12)=tan(8π/12)=tan(2π/3)=根號(hào)3 ；