4) \(\frac{\sqrt{65} \cdot \sqrt{13}}{\sqrt{5}}\)

1. \(\frac{\sqrt{5 \cdot 13} \cdot \sqrt{13}}{\sqrt{5}}\) = \(\frac{\sqrt{5} \cdot \sqrt{13} \cdot \sqrt{13}}{\sqrt{5}}\).
2. \(\sqrt{13}\) \(\cdot\) \(\sqrt{13}\) = 13.
3. \(\text{Ответ: }\) 13.