Identidades trigonometricas

sen²x + cos²x = 1
1 + tg²x = sec²x
1 + ctg²x = cosec²x
tg x = sen x / cos x
cosec x = 1 / sen x
sec x = 1 / cos x
ctg x = 1/ tan x = cosx/senx
1 + cotg²a = cosec²a
sen (a +- b) = sena · cosb +- cosa· senb
cos (a +- b) = cosa · cosb -+ sena· senb
sen(2a) = 2sena · cosa
cos(2a) = cos²a - sen²a

tg2a = 2tga / 1-tg²a
sen(a/2) = ?1-cosa/2

cos(a/2)=?1+cosa/2
tg(a/2) = ?1-cosa/1+cosa
senA+senB =2 · sen(A+B)/2 · cos(A-B)/2
senA-senB =2 · cos (A+B)/2· sen(A-B)/2
cosA+cosB =2 · cos(A+B)/2 · cos(A-B)/2
cosA-cosB =-2 · sen(A+B)/2 · sen(A-B)/2