\[x^{2} - 9x + 8 = (x - 8)(x - 1)\]
\[D = 81 - 32 = 49\]
\[x_{1} = \frac{9 + 7}{2} = 8;\text{\ \ \ }x_{2} = \frac{9 - 7}{2} = 1.\]
\[Ответ:x^{2} - 9x + 8 = (x - 8)(x - 1).\]