Вычислить cos105sin35-cos145cos15/sin^2 25-cos^2 45

Cos(90+15)sin35-cos(180-35)cos15)/(sin²25-cos²45)=
=(-sin15sin35+cos35cos15)/(sin²25-cos²45)=
=cos(35+15)/(sin²25-cos²45)=
=cos50:[(1-cos50)/2-(1+cos90)/2]=cos50/(1/2-1/2*cos50-1/2)=
=cos50:(-1/2)cos50=-2