13.1. \((\sqrt{27}-\sqrt{3})\cdot\sqrt{3}\)

\(\sqrt{27}=3\sqrt{3}\).

\((\sqrt{27}-\sqrt{3})\cdot\sqrt{3}=(3\sqrt{3}-\sqrt{3})\cdot\sqrt{3}=2\sqrt{3}\cdot\sqrt{3}=2\cdot3=6\).

Ответ: \(6\)