question_answer

If \[\cos \,(\alpha +\beta )=0\] and \[\sin \,(\alpha -\beta )=\frac{1}{2},\] then find the value of\[\frac{\cos 2\beta }{\sin \,(\alpha /2)}\].

A)  0                                

B)  1

C)  \[-\,1\]                         

D)  4

E)  None of these