\[(10 - 2a)x^{2} - (a - 5)x + 1 = 0,\ \ \ \ \]
\[a = 5\]
\[D = a^{2} - 10a + 25 - 40 + 8a =\]
\[= a^{2} - 2a - 15 < 0\]
\[a^{2} - 2a - 15 = 0\]
\[a_{1} + a_{2} = 2\ \ \ \ \ \ \ a_{1} = 5\]
\[a_{1}a_{2} = - 15\ \ \ \ \ \ \ a_{2} = - 3\ \]
\[Ответ:при\ a \in ( - 3;\ \ \ 5\rbrack.\]