Ответ:

  1. \(\sqrt{2}\cdot\sqrt{2}=2\).
  2. \(\sqrt{3}\cdot\sqrt{3}=3\).
  3. \(2\sqrt{3}\cdot\sqrt{3}=2\cdot3=6\).
  4. \(4\sqrt{5}\cdot\sqrt{5}=4\cdot5=20\).
  5. \(3\sqrt{2}\cdot2\sqrt{2}=3\cdot2\cdot2=12\).
  6. \(5\sqrt{7}\cdot3\sqrt{7}=5\cdot3\cdot7=105\).