Identities

Basic Identities

sin2 θ = 1 − cos2 θ

cos2 θ = 1 − sin2 θ

tan2 θ + 1 = sec2 θ

tan2 θ = sec2 θ − 1

cot2 θ + 1 = csc2 θ

cot2 θ = csc2 θ − 1

Compound Identities

Note that  means you can use plus or minus, and the  means to use the opposite sign.

Double Angle Identities

Half Angle Identities

Note that "±" means it may be either one, depending on the value of θ/2