Ответ:\(\sqrt{0.25\cdot81}=\sqrt{20.25}=4.5\).\(\sqrt{16\cdot900}=\sqrt{14400}=120\).\(\sqrt{49\cdot121}=\sqrt{5929}=77\).\(\sqrt2\cdot\sqrt8=\sqrt{16}=4\).\(\sqrt5\cdot\sqrt{20}=\sqrt{100}=10\).