Ta có:
\(\sqrt{6}+\sqrt[3]{6}< \sqrt{6+\sqrt{6+...+\sqrt{6}}}+\sqrt[3]{6+\sqrt[3]{6+...+\sqrt[3]{6}}}< \sqrt{6+\sqrt{6+...+\sqrt{9}}}+\sqrt[3]{6+\sqrt[3]{6+...+\sqrt[3]{8}}}\)
\(\Leftrightarrow4< \sqrt{6}+\sqrt[3]{6}< \sqrt{6+\sqrt{6+...+\sqrt{6}}}+\sqrt[3]{6+\sqrt[3]{6+...+\sqrt[3]{6}}}< 3+2\)
\(\Leftrightarrow4< \sqrt{6+\sqrt{6+...+\sqrt{6}}}+\sqrt[3]{6+\sqrt[3]{6+...+\sqrt[3]{6}}}< 5\)