\[\boxed{\text{648\ (648).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[= 25\]
\[x_{1,2} = \frac{4k + 1 \pm 5}{2}\]
\[x_{1} = \frac{4k + 1 + 5}{2} = \frac{4k + 6}{2} =\]
\[= 2k + 3\]
\[x_{2} = \frac{4k + 1 - 5}{2} = \frac{4k - 4}{2} =\]
\[= 2k - 2\ \]
\[Ответ:x = 2k + 3;\ \ x = 2k - 2.\]