Quels que soient les nombres aaa et bbb :
cos(a+b)=cosacosb−sinasinb\cos (a + b) = \cos a \cos b − \sin a \sin bcos(a+b)=cosacosb−sinasinb
cos(a−b)=cosacosb+sinasinb\cos (a − b) = \cos a \cos b + \sin a \sin bcos(a−b)=cosacosb+sinasinb
sin(a+b)=sinacosb+sinbcosa\sin (a + b) = \sin a \cos b + \sin b \cos asin(a+b)=sinacosb+sinbcosa
sin(a−b)=sinacosb−sinbcosa\sin (a − b) = \sin a \cos b − \sin b \cos asin(a−b)=sinacosb−sinbcosa
cos2a=cos2a−sin2a=2cos2a−1=1−2sin2a\cos 2a = \cos^2 a − \sin^2a = 2 \cos^2 a − 1 = 1 − 2 \sin^2 acos2a=cos2a−sin2a=2cos2a−1=1−2sin2a
sin2a=2sinacosa\sin2a = 2 \sin a \cos asin2a=2sinacosa.