# Math Help - Trigo-equation

1. ## Trigo-equation

Find all reals numbers a , b solutions for equation :

$\sin (3a + b) + \sin (3a - b) + \sin (a - b) - \sin (a + b) = \cos (b)$

2. is not this the right form? sin (3A + B) + sin (3A - B) - sin (A - B) - sin (A + B) = cos B,

4 sin A cos 2A = 1,

plot of 4 sin A cos 2A - 1 = 0,

6 roots i think . . . .

why do angle B vanishes in my equation?