\[\left( 5\sqrt{2} - \sqrt{18} \right) \cdot \sqrt{2} =\]
\[= 5\sqrt{2} \cdot \sqrt{2} - \sqrt{18} \cdot \sqrt{2} =\]
\[= 5 \cdot 2 - \sqrt{36} = 10 - 6 = 4.\]