Cos72+cos12/sin12-sin72

Question

Cos72+cos12/sin12-sin72

Answer 1

Cos72 + cos12 = 2 cos (72 + 12)/2 * cos (72 - 12)/2 = 
 = 2 cos 42 * cos 30

sin12 - sin72 = 2 sin (12 - 72)/2 * cos (12 + 72)/2 = 
= - 2 sin30 * cos 42

(2 cos 42 * cos 30) / (- 2 sin30 * cos 42 ) = 
= (cos 30) / ( -  sin30 ) = 
= - ctg30 = - √3

Ответ
- √3