\[x^{4} - 24x^{2} - 25 = 0\]
\[Пусть\ t = x^{2} \geq 0:\]
\[t^{2} - 24t - 25 = 0\]
\[t_{1} + t_{2} = 24;\ \ \ \ t_{1} \cdot t_{2} = - 25\]
\[t_{1} = 25;\ \ \ \ t_{2} = - 1.\]
\[Подставим:\ \]
\[x^{2} = 25\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ x^{2} = - 1\]
\[x = \pm 5\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ нет\ решения.\]
\[Ответ:\ x = \pm 5.\]