dy/dx=(1+y^2)/[xy(1+x^2)]y/(1+y^2)dy=dx/[x(1+x^2)]2y/(1+y^2)dy=2xdx[x^2(1+x^2)]d(y^2)/(1+y^2)=d(x^2)[1/x^2-1/(1+x^2)]ln(1+y^2)=ln(x^2)-ln(1+x^2)+C11+y^2=Cx^2/(1+x^2)