\[x^{2} + \frac{25}{x^{2}} = 54;\ \ x + \frac{5}{x} = ?\]
\[x^{2} + 2x \cdot \frac{5}{x} + \left( \frac{5}{x} \right)^{2} = 54 + 2x \cdot \frac{5}{x}\]
\[\left( x + \frac{5}{x} \right)^{2} = 54 + 10\]
\[\left( x + \frac{5}{x} \right)^{2} = 64\]
\[x + \frac{5}{x} = 8;\]
\[x + \frac{5}{x} = - 8.\]
\[Ответ:\ - 8;8.\]