Question

please answer it fast...

prove that it is equal to 0

Answer 1

[2 * sin(3A+A)/2 * cos(3A-A)/2] sin A + [-2 * sin(3A+A)/2 * sin(3A-A)/2] cosA
(sin c + sin d and cos c+ cos d formula used above)
=[2sin2A*cosA] sin A - [2sin2A*sinA]cos A
=2sinA*sin 2A*cosA - 2 sinA*sin2A*cos A
=0

hope this helps!