\[\frac{x - 1}{x + a} = 0;\ \ \ \ x \neq - a\]
\[x - 1 = 0\ \ \]
\[x = 1.\]
\[a = - 1 \Longrightarrow нет\ решения\]
\[a \neq - 1 \Longrightarrow x = 1.\]