question_answer

If Sin 2\[\alpha \] = 2 Sin\[\alpha \] Cos \[\alpha \] and Sin \[\mathbf{40}{}^\circ \] = m, then the value of Cos\[\mathbf{8}{{\mathbf{0}}^{\mathbf{o}}}\], Cos\[\mathbf{160}{}^\circ \], is equal to

A)  \[\frac{1}{4}\]                                                             

B)  \[\frac{1}{8}\]          

C)  \[\frac{-1}{8}\]     

D) \[\frac{-1}{4}\]

E) None of these