Đặt [TEX]A=\sqrt{8+2\sqrt{10+2\sqrt{5}}}+\sqrt{8-2\sqrt{10+2\sqrt{5}}}[/TEX]
[TEX]\Rightarrow A^2=8+2\sqrt{10+2\sqrt{5}}+8-2\sqrt{10+2\sqrt{5}}+2\sqrt{(8+2\sqrt{10+2\sqrt{5}})(8-2\sqrt{10+2\sqrt{5}})}[/TEX]
[TEX]=16+2\sqrt{64-4(10+2\sqrt{5}}[/TEX]
[TEX]=16+2\sqrt{20-8\sqrt{5}+4}[/TEX]
[TEX]=16+2(\sqrt{20}-2}[/TEX]
[TEX]=12+\sqrt{20}[/TEX]
A>0 \Rightarrow [TEX]A=\sqrt{12+\sqrt{20}}=\sqrt{2}.\sqrt{6+2\sqrt{5}}[/TEX]
[TEX]=\sqrt{2}(\sqrt{5}+1)[/TEX]