sin2a = 2 sina cosa
sina = 2 sin (a) cos (a)
cos2a = cos2a - sin2a =
= 1 - 2sin2a =
= 2cos2a - 1
tg2a = 2 tga
1 - tg2a
= 2
ctga - tga
tga = 2 tg (a/2)
1 - tg2 (a/2)
ctg2a = ctg2a - 1
2 ctga
= ctga - tga
ctga = ctg2 (a/2) - 1
2 ctg (a/2)
sin x = a
x = (-1)n arksin a + pn
cos x = a
x = ± arkcos a + 2pn
tg x = a
x = arktg a + pn
ctg x = a
x = arkctg a + pn