question_answer

sIf \[f(x)=\cos (\log x)\], then \[f(x)f(y)-\frac{1}{2}[f(x/y)+f(xy)]=\] [IIT 1983; RPET 1995; MP PET 1995; Karnataka CET 1999; UPSEAT 2001]

A)            \[-1\]

B)            \[\frac{1}{2}\]

C)            \[-2\]

D)            None of these