$4 = \sqrt{16}$
$\sqrt{5} < \sqrt{16}$
$\sqrt{5} < 4$
тогда:
$\sqrt{(\sqrt{5} - 4)^2} = |\sqrt{5} - 4| = 4 - \sqrt{5}$

$3 = \sqrt{9}$
$\sqrt{8} < \sqrt{9}$
$\sqrt{8} < 3$
$\sqrt{2} < \sqrt{9}$
$\sqrt{2} < 3$
тогда:
$\sqrt{(\sqrt{8} - 3)^2} - \sqrt{(\sqrt{2} - 3)^2} = |\sqrt{8} - 3| - |\sqrt{2} - 3| = 3 - \sqrt{8} - (3 - \sqrt{2}) = 3 - \sqrt{8} - 3 + \sqrt{2} = \sqrt{2} - \sqrt{8} = \sqrt{2} - \sqrt{4 * 2} = \sqrt{2} - 2\sqrt{2} = -\sqrt{2}$