1) sin 420° = sin (360° + 60°) = sin 60° = √3/2
2) cos 11π/6 = cos (2π - π/6) = cos (-π/6) = cos π/6 = √3/2
3) tg 31π/3 = tg (10π + π/3) = tg π/3 = √3
4) ctg (-330°) = - ctg 330° = - ctg (360° - 30°) = - ctg (-30°) = ctg 30° = √3
