\[\sqrt{2} + \sqrt{5} > \sqrt{7}\ \]
\[\left( \sqrt{2} + \sqrt{5} \right)^{2} = 2 + 2\sqrt{10} + 5 =\]
\[= \ 7 + 2\sqrt{10}\]
\[\left( \sqrt{7} \right)^{2} = 7\]
\[7 + 2\sqrt{10} > 7\]
\[\Longrightarrow \sqrt{2} + \sqrt{5} > \sqrt{7}.\]