\[\boxed{\text{477}\text{\ (477)}\text{.}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[x^{2} = a\]
\[1)\ a = 4:\]
\[x^{2} = 4\]
\[x = 2\ и\ x = - 2.\]
\[2)\ a = 5:\ \]
\[x^{2} = 5\]
\[x = \sqrt{5}\ и\text{\ x} = - \sqrt{5}.\]
\[3)\ a = - 2:\ \ \]
\[x^{2} = - 2\]
\[нет\ корней.\ \ \]