\[\boxed{\mathbf{738\ (738).\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
\[\frac{x_{1}}{x_{2}} + \frac{x_{2}}{x_{1}} = \frac{5}{2}\]
\[\frac{x_{1}^{2} + x_{2}^{2}}{x_{1}x_{2}} = \frac{\left( x_{1} + x_{2} \right)^{2} - 2x_{1}x_{2}}{x_{1}x_{2}} =\]
\[= \frac{5}{2}\]
\[x^{2} - ax + 8 = 0\]
\[x_{1} \cdot x_{2} = 8\]
\[x_{1} + x_{2} = a\]
\[\frac{a^{2} - 16}{8} = \frac{5}{2}\]
\[a^{2} - 16 = 20\]
\[a^{2} = 36\]
\[a = 6;\ \ \ \ a = - 6\]
\[Ответ:a = 6\ или\ a = - 6.\]
\[\boxed{\mathbf{7}\mathbf{3}\mathbf{8}\mathbf{\text{.\ }}Еуроки\ - \ ДЗ\ без\ мороки}\]
\[1)\ 53 - 24 - 1 = 28\ (страниц)\]
\[- номера,\ которых\ не\ хватает.\]
\[2)\ 28\ :2 = 14\ листов\ \]
\[не\ хватает.\]
\[Ответ:14\ листов.\]