Question

sin7n/12cosn/12-sinn/12cos7n/12=

Answer 1

Синус разности  углов
sin(7pi/12) * cos (pi/12) - sin(pi/12) * cos (7pi/12) =
 = sin  ( 7pi/12 - pi/12) = sin ( 6pi/12) = sin ( pi/2) = 1