\(\color{blue} 2\sin \text {A} \cos \text {B} = \sin (\text{A + B}) + \sin (\text{A − B})\)
\(\color{blue} 2\cos \text {A} \sin \text {B} = \sin (\text{A + B})\:-\: \sin (\text{A − B})\)
\(\color{blue} 2\cos \text {A} \cos \text {B} = \cos (\text{A + B}) + \cos (\text{A − B})\)
\(\color{blue} -2\sin \text {A} \sin \text {B} = \cos (\text{A + B}) \:-\: \cos (\text{A − B})\)