\[x^{4} + 25x^{2} = 0\]
\[x^{2}\left( x^{2} + 25 \right) = 0\]
\[x^{2} = 0;\ \ \ \ \ \ \ \ \ x^{2} + 25 = 0\]
\[x = 0\ \ \ \ \ \ \ \ \ \ \ \ нет\ корней\]
\[Ответ:x = 0.\]