13.4. \((\sqrt{50}-\sqrt{2})\cdot\sqrt{2}\)

\(\sqrt{50}=5\sqrt{2}\).

\((\sqrt{50}-\sqrt{2})\cdot\sqrt{2}=(5\sqrt{2}-\sqrt{2})\cdot\sqrt{2}=4\sqrt{2}\cdot\sqrt{2}=4\cdot2=8\).

Ответ: \(8\)