\[\left( a^{2} - a - 56 \right)x = a² - 64\]
\[a^{2} - a - 56 = 0\]
\[a_{1} + a_{2} = 1;\ \ a_{1} \cdot a_{2} = - 56\]
\[\Longrightarrow a_{1} = 8,\ \ a_{2} = - 7.\]
\[a^{2} - a - 56 = (a - 8)(a + 7)\]
\[(a - 8)(a + 7)x =\]
\[= (a - 8)(a + 8)\]
\[a = - 7 \Longrightarrow нет\ решения;\]
\[a = - 8 \Longrightarrow x = 0;\]
\[a \neq - 7;a \neq \pm 8 \Longrightarrow x = \frac{a + 8}{a + 7};\]
\[a = 8:\]
\[\left( 8^{2} - 8 - 56 \right)x = 8^{2} - 64\]
\[0 \cdot x = 0 \Longrightarrow x - любое.\]