(cos42.5°*cos8.5°- sin42.5°*sin8.5°)/(cos12°sin42°-cos42*sin12°)=
(cos(42.5°+8.5°))/sin(42°-12°)=cos51°/sin30°=2cos51°
(cos42.5°*cos8.5°- sin42.5°*sin8.5°)/(cos12°sin42°-cos42*sin12°)=
(cos(42.5°+8.5°))/sin(42°-12°)=cos51°/sin30°=2cos51°