(cos75*cos15-cos15*cos105) / (sin18*sin63+sin108*sin27)

(cos75*cos15-cos15*cos105) / (sin18*sin63+sin108*sin27)=(сos (90-15) cos15-cos15cos (90-15) / (sin (90+18) sin27+sin18sin (90-27)=(sin15cos15+cos15sin15) / (cos18sin27+sin18cos27)=sin30/sin (45)=(1/2) / (sqrt (2) /2)=sqrt (2) /2