$(x+\sqrt{x^2+5}).(\sqrt{x^2+5}-x).(y+\sqrt{y^2+5})(\sqrt{y^2+5}-y)=25$$\Rightarrow (\sqrt{x^2+5}-x)(\sqrt{y^2+5}-y)=5$roi giai tim x+y
$(x+\sqrt{x^2+5}).(\sqrt{x^2+5}-x).(y+\sqrt{y^2+5})(\sqrt{y^2+5}-y)=25$$\Rightarrow (\sqrt{x^2+5}-x)(\sqrt{y^2+5}-y)=5=(x+\sqrt{x^2+5}).(y+\sqrt{y^2+5})$roi giai tim2 x+y
$(x+\sqrt{x^2+5}).(\sqrt{x^2+5}-x).(y+\sqrt{y^2+5})(\sqrt{y^2+5}-y)=25$$\Rightarrow (\sqrt{x^2+5}-x)(\sqrt{y^2+5}-y)=5$roi giai tim x+y