\[y = ax^{2} - (a - 3)x + 1;\ \ \ \ D = 0\]
\[D = a^{2} - 6a + 9 - 4a =\]
\[= a^{2} - 10a + 9\]
\[a^{2} - 10a + 9 = 0\]
\[a_{1} + a_{2} = 10\ \ \ \ \ \ a_{1} = 9\]
\[a_{1} \cdot a_{2} = 9\ \ \ \ \ \ \ \ \ \ \ a_{2} = 1\]
\[Ответ:при\ a = 9;\ \ a = 1.\]