b/ [tex]\sqrt{32-4\sqrt{60}}=2\sqrt{2}.\sqrt{4-\sqrt{15}}=2\sqrt{2}.\frac{(\sqrt{4-\sqrt{15}})(\sqrt{4+\sqrt{15}})}{\sqrt{4+\sqrt{15}}}=2\sqrt{2}.\frac{1}{\sqrt{4+\sqrt{15}}}[/tex]
Suy ra [tex]\sqrt{32-4\sqrt{60}}-\sqrt{\frac{2}{4+\sqrt{15}}}=\frac{2\sqrt{2}}{\sqrt{4+\sqrt{15}}}-\frac{\sqrt{2}}{\sqrt{4+\sqrt{15}}}=\frac{\sqrt{2}}{\sqrt{4+\sqrt{15}}}[/tex]