4Ta có$:(\sqrt{10-6\sqrt{2}}-\sqrt{10+6\sqrt{2}})^2=20-2\sqrt{(10-6\sqrt{2})(10+6\sqrt{2})}=20-2\sqrt{100-72}=20-4\sqrt{7}$$\Rightarrow \sqrt{10-6\sqrt{2}}-\sqrt{10+6\sqrt{2}}=-\sqrt{20-4\sqrt{7}}$
Ta có:
$H=-\frac{\sqrt{4(5-\sqrt{7})}}{\sqrt{5-\sqrt{7}}}-\sqrt{2^2-2.2.\sqrt{5}+(\sqrt{5})^2}=-\sqrt{4}-\sqrt{(\sqrt{5}-2)^2}=-2-\sqrt{5}+2=-\sqrt{5}$