13) √20 + √500 + √3 =

\(\sqrt{20}=2\sqrt{5}\), а \(\sqrt{500}=10\sqrt{5}\).

\(2\sqrt{5}+10\sqrt{5}+\sqrt{3}=12\sqrt{5}+\sqrt{3}\).

Ответ: \(12\sqrt{5}+\sqrt{3}\).