x't=2ty't=1-1/(1+t^2)=t^2/(1+t^2)y'=dy/dx=y't/x't=t/[2(1+t^2)]d^y/dx^2=d(y')/dx=d(y')/dt/x't=1/2*[1+t^2-2t^2]/(1+t^2)^2/(2t)=(1-t^2)/[4t(1+t^2)^2]
