Trigonometric Double and Half Angle Identities

sin2x

2sinxcosx

cos2x (sin & cos)

cos²x-sin²x

cos2x (cos)

2cos²x-1

cos2x (sin)

1-2sin²x

tan2x

2tanx/(1-tan²x)

cos(x/2)

±√(1+cosx)/2

sin(x/2)

±√(1-cosx)/2

tan(x/2) (cos sqrt)

±√(1-cosx)/(1+cosx)

tan(x/2) (sin cos)

sinx/(1+cosx)

tan(x/2) (cos sin)

(1-cosx)/sinx