\[\boxed{\text{484}\text{\ (484)}\text{.}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[1)\ неверно:\]
\[\sqrt{2} + \left( - \sqrt{2} \right) = 0.\]
\[2)\ неверно:\]
\[\sqrt{2} \cdot \sqrt{2} = \left( \sqrt{2} \right)^{2} = 2.\]
\[3)\ неверно:\]
\[\sqrt{2} \cdot 0 = 0.\ \]