\[\boxed{\mathbf{551\ (551).\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
\[1)\ 0,5\sqrt{12} - 3\sqrt{27} + 0,4\sqrt{75} =\]
\[= \sqrt{3} - 9\sqrt{3} + 2\sqrt{3} = - 6\sqrt{3};\]
\[= 5\sqrt{7b} + 2\sqrt{7b} - \sqrt{7b} = 6\sqrt{7b};\]
\[3)\ \sqrt{81a^{7}} - 5a^{3}\sqrt{a} + \frac{6}{a}\sqrt{a^{9}} =\]
\[= 9a^{3}\sqrt{a} - 5a^{3}\sqrt{a} + 6a^{3}\sqrt{a} =\]
\[= 10a^{3}\sqrt{a}.\]
\[\boxed{\mathbf{5}\mathbf{5}\mathbf{1}\mathbf{\text{.\ }}Еуроки\ - \ ДЗ\ без\ мороки}\]
\[1)\frac{2}{3}\sqrt{45} = \frac{2}{3} \cdot 3\sqrt{5} = 2\sqrt{5};\]
\[2)\frac{1}{2}\sqrt{128} = \frac{1}{2} \cdot 8\sqrt{2} = 4\sqrt{2};\]
\[3)\frac{1}{10}\sqrt{200} = \frac{1}{10} \cdot 10\sqrt{2} = \sqrt{2};\]
\[4) - 0,05\sqrt{4400} =\]
\[= - 0,05 \cdot 20\sqrt{11} = - \sqrt{11}.\]