2/x-1/y=3
(2y-x)/(xy)=3
xy/(x-2y)=-1/3
{(y/x)-[y/(x-y)]*[(x-y)/x-x+y]}/[(x-2y)/x]
={y/x-[y/(x-y)*(x-y)/x]+[y/(x-y)*(x-y)]}*x/(x-2y)
=(y/x-y/x+y)*x/(x-2y)
=xy/(x-2y)
=-1/3