Rinkoo Gupta
Last Activity: 10 Years ago
solution no.3
f(x)
cos(lnx)
so f(x)f(y)-1/2[f(x/y)+f(xy)]
=cos(lnx)cos(lny)-1/2{cos(ln(x/y))+cos(ln(xy))}
=1/2[2 cos(lnx)cos(lny)-{cos(ln(x/y))+cos(ln(xy))}]
=1/2[{cos(lnx+lny)+cos(lnx-lny)}-{cos(lnx/y))+cos(ln(xy))}]
=1/2[cos(ln(xy))+cos(ln(x/y))-cos(ln(x/y))-cos(ln(xy))]
=0
Thanks & Regards
Rinkoo Gupta
AskIITians Faculty