question_answer

If \[f(x)=\cos \,\,(\log x),\] then \[f(x)f(y)-\frac{1}{2}[f(x\text{/}y)+f(xy)]=\]

A)  \[-1\]                           

B)  \[\frac{1}{2}\]

C)  \[-2\]                           

D)  All of these

E)  None of these