Useful trigonometric identities

1. Some useful (?) trigonometric identities
2 2
sin cos 1A A+ = ( )sin 2 cosA Aπ − =
( )sin sinA A− =−
( )cos cosA A− =
( )tan tanA A− =−
( )sin sin cos cos sinA B A B A B±= ±
( )cos cos cos sin sinA B A B A B± = 
( )
tan tan
tan
1 tan tan
A B
A B
A B
±
± =

( )sin 2 2sin cosA A A=
( ) 2 2 2
cos 2 cos sin 1 2sinA A A A= − =−
( ) 2
2tan
tan 2
1 tan
A
A
A
=
−

2. More useful (?) trigonometric identities
sin sin 2sin cos
2 2
A B A B
A B
+ −   
+ =   
   
sin sin 2cos sin
2 2
A B A B
A B
+ −   
− =   
   
cos cos 2cos cos
2 2
A B A B
A B
+ −   
+ =   
   
cos cos 2sin sin
2 2
A B A B
A B
+ −   
− =−    
   
( ) ( )1
2sin sin cos cosA B A B A B = − − + 
( ) ( )1
2cos cos cos cosA B A B A B = − + + 
( ) ( )1
2sin cos sin sinA B A B A B = + + − 
( ) ( )1
2cos sin sin sinA B A B A B = + − − 