Question

___sinb=1/2[sin(a+b) - sin(a-b)]

Answer 1

hint: page 2

http://tutorial.math.lamar.edu/pdf/Trig_Cheat_Sheet.pdf

Answer 2

\[\sin \left( a+b \right)=\sin a \cos b+\cos a \sin b\]
\[\sin \left( a-b \right)=\sin a \cos b-\cos a \sin b\]
subtract and get the answer