$9)\sqrt{5+2\sqrt{6}}-\sqrt{5-2\sqrt{6}}$
$=\sqrt{(\sqrt{3}+\sqrt{2})²}-\sqrt{(\sqrt{3}-\sqrt{2})²}$
$=\sqrt{3}+\sqrt{2}-\sqrt{3}+\sqrt{2}$
$=2\sqrt{2}$
$10)\sqrt{7+4\sqrt{3}}-\sqrt{9+4\sqrt{5}}-\sqrt{21-8\sqrt{5}}$
$=\sqrt{(2+\sqrt{3})²}-\sqrt{(\sqrt{5}+2)²}-\sqrt{(4-\sqrt{5})²}$
$=2+\sqrt{3}-\sqrt{5}-2-4+\sqrt{5}$
$=-4+\sqrt{3}$
