-0.4472135955 sin (arcctg(-2))
arcsin(cos( пи/9)) = arcsin (cos( пи/2-7пи/18)) = arcsin(sin(7пи/18)) = 7пи/18
-0.4472135955 sin (arcctg(-2))
arcsin(cos( пи/9)) = arcsin (cos( пи/2-7пи/18)) = arcsin(sin(7пи/18)) = 7пи/18