\[x^{4} + 16x^{2} = 0\]
\[x^{2}\left( x^{2} + 16 \right) = 0\]
\[x^{2} = 0;\ \ \ \ \ \ x^{2} = - 16\]
\[x = 0\ \ \ \ \ \ \ \ \ \ нет\ корней.\]
\[Ответ:x = 0.\]