формулы двойного аргумента

cos 2x = cos²x – sin² x = 2 cos² x -1 = 1 – 2 sin² x = 1 – tg² x/1 + tg² x

sin 2x = 2 sin x · cos x = 2 tg x/ 1 + tg² x

tg 2x = 2 tg x/ 1 – tg² x

ctg 2x = ctg ² x – 1/ 2 ctg x

sin 3x = 3 sin x – 4 sin³ x

cos 3x = 4 cos³ x – 3 cos x

tg 3x = 3 tg x – tg³ x / 1 – 3 tg² x

sin s cos t = (sin (s+t) + sin (s+t))/2

sin s sin t = (cos (s-t) - cos (s+t))/2

cos s cos t = (cos (s+t) + cos (s-t))/2