Let’s find horizontal asymptotes with help of the limits of this function at x->+oo and x->-oo
$$\lim_{x \to -\infty}\left(- x + \left(\left(x + \sqrt{10}\right) - \sqrt{2}\right)\right) = - \sqrt{2} + \sqrt{10}$$
Let's take the limitso,
equation of the horizontal asymptote on the left:
$$y = - \sqrt{2} + \sqrt{10}$$
$$\lim_{x \to \infty}\left(- x + \left(\left(x + \sqrt{10}\right) - \sqrt{2}\right)\right) = - \sqrt{2} + \sqrt{10}$$
Let's take the limitso,
equation of the horizontal asymptote on the right:
$$y = - \sqrt{2} + \sqrt{10}$$