Помогите плиз Cos50*cos 20-sin50*sin20/cos 85*cos 15+sin 85*sin15

Question

Помогите плиз
Cos50*cos 20-sin50*sin20/cos 85*cos 15+sin 85*sin15

Answer 1

(cos50.cos20-sin50sin20)/(cos85cos15+sin85sin15)=
=cos(50+20)/cos(85-15))=cos70/cos70 =1

cos(x+y)=cosxcosy-sinxsiny
cos(x-y)=cosxcosysinxsiny