13.2. \((\sqrt{8}-\sqrt{2})\cdot\sqrt{2}\)

\(\sqrt{8}=2\sqrt{2}\).

\((\sqrt{8}-\sqrt{2})\cdot\sqrt{2}=(2\sqrt{2}-\sqrt{2})\cdot\sqrt{2}=\sqrt{2}\cdot\sqrt{2}=2\).

Ответ: \(2\)