Đặt A=\(\sqrt{4+\sqrt{10+2\sqrt{5}}}\)+\(\sqrt{4-\sqrt{10+2\sqrt{5}}}\)
\(\Rightarrow\) A2=4+\(\sqrt{10+2\sqrt{5}}\)+2\(\sqrt{16-10+2\sqrt{5}}\)+4-\(\sqrt{10+2\sqrt{5}}\)
=8+2\(\sqrt{6+2\sqrt{5}}\)
=8+2(\(\sqrt{5}\)+1) =8+2\(\sqrt{5}\)+2=10+2\(\sqrt{5}\)
\(\Rightarrow\) A=\(\sqrt{10+2\sqrt{5}}\)