1.

If `f(x)=cos (logx)`, then `f(x)f(y)-1/2[f(x/y)+f(xy)]=`A. -1B. `1//2`C. -2D. 0

Answer» Correct Answer - D
`f(x)=cos(logx)`
or `f(x)f(y)-(1)/(2)[f((x)/(y))+f(xy)]`
`=cos(logx)cos(logy)-(1)/(2)[cos(logx-logy)]+[cos(logx+logy)]`
`=cos(logx)cos (logy)-(1)/(2)[2cos(logx)cos(logy)]`
`=0`


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