\[\boxed{\mathbf{510\ (510).\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
\[1)\ \sqrt{b^{2}} = |b|;\]
\[2) - 0,4 \cdot \sqrt{c^{2}} = - 0,4 \cdot |c|;\]
\[3)\ \sqrt{a^{6}} = \left| a^{3} \right|;\]
\[4)\ \sqrt{m^{8}} = \left| m^{4} \right|.\]
\[\boxed{\mathbf{51}\mathbf{0}\text{.}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[1)\ неверно:\]
\[\sqrt{2} + \left( - \sqrt{2} \right) = 0.\]
\[2)\ неверно:\]
\[\sqrt{2} \cdot \sqrt{2} = \left( \sqrt{2} \right)^{2} = 2.\]
\[3)\ неверно:\]
\[\sqrt{2} \cdot 0 = 0.\ \]