Lời giải:
\(\sqrt{20+4\sqrt{10}+4\sqrt{15}+4\sqrt{6}}=\sqrt{20+4\sqrt{15}+4(\sqrt{10}+\sqrt{6})}\)
\(=\sqrt{4+10+6+2\sqrt{6.10}+4(\sqrt{10}+\sqrt{6})}\)
\(=\sqrt{4+(\sqrt{6}+\sqrt{10})^2+4(\sqrt{10}+\sqrt{6})}\)
\(=\sqrt{(\sqrt{6}+\sqrt{10}+2)^2}=2+\sqrt{6}+\sqrt{10}\)