\[x^{4} - 35x^{2} - 36 = 0\]
\[x^{2} = y \geq 0:\]
\[y^{2} - 35y - 36 = 0\]
\[y_{1} + y_{2} = 35;\ \ y_{1} \cdot y_{2} = - 36\]
\[y_{1} = 36;\ \ y_{2} = - 1 < 0.\]
\[x^{2} = 36\]
\[x = \pm 6.\]
\[Ответ:x = \pm 6.\]