\[\left( a^{2} - 4a - 5 \right)x = a² - 25\]
\[a^{2} - 4a - 5 = 0\]
\[a_{1} + a_{2} = 4;\ \ a_{1} \cdot a_{2} = - 5\]
\[a_{1} = 5,\ \ a_{2} = - 1\]
\[a^{2} - 4a - 5 = (a - 5)(a + 1).\]
\[1)\ \ a = 5:\]
\[\left( 5^{2} - 4 \cdot 5 - 5 \right)x = 5^{2} - 25\ \ \]
\[0 \cdot x = 0\]
\[\Longrightarrow x - любое.\]
\[2)\ a = - 5:\]
\[x = \frac{- 5 + 5}{- 5 + 11} = \frac{0}{- 4} = 0.\]
\[3)\ \ a = - 1:\]
\[нет\ решения.\]
\[4)\ \ a \neq \pm 5;a \neq - 1:\]
\[x = \frac{a + 5}{a + 1}.\]