Question
Let A and B denote the statements
A: $\cos \alpha + \cos \beta + \cos \gamma = 0$
B: $\sin \alpha + \sin \beta + \sin \gamma = 0$
If $\cos \left( {\beta - \gamma } \right) + \cos \left( {\gamma - \alpha } \right) + \cos \left( {\alpha - \beta } \right) = - {3 \over 2},$ then: