Respuesta :

Answer:

[tex]\textbf{A.} \cos b[/tex]

Step-by-step explanation:

[tex]\dfrac 12 \left[\sin(a+b)+\sin(a-b) \right]\\\\\\=\dfrac 12\left[ 2 \sin a \cos b\right]\\\\\\=\sin a \cos b[/tex]