2. \(\frac{\sqrt{35}\cdot\sqrt{21}}{\sqrt{15}}\); 4. \(\frac{\sqrt{65}\cdot\sqrt{13}}{\sqrt{5}}\); 6. \(\frac{\sqrt{75}\cdot\sqrt{10}}{\sqrt{30}}\)

1. \(\frac{\sqrt{35}\cdot\sqrt{21}}{\sqrt{15}}=\sqrt{\frac{35\cdot21}{15}}=\sqrt{49}=7\).
2. \(\frac{\sqrt{65}\cdot\sqrt{13}}{\sqrt{5}}=\sqrt{\frac{65\cdot13}{5}}=\sqrt{169}=13\).
3. \(\frac{\sqrt{75}\cdot\sqrt{10}}{\sqrt{30}}=\sqrt{\frac{75\cdot10}{30}}=\sqrt{25}=5\).

Ответ: 2) 7; 4) 13; 6) 5.