\[\sqrt{a(x - 1)} = 0\ \ \]
\[a(x - 1) = 0\]
\[x - 1 = 0\]
\[x = 1.\]
\[a = 0 \Longrightarrow x - любое.\]
\[a \neq 0 \Longrightarrow x = 1.\]