\[\frac{x - a}{x^{2} - 4x + 3} = 0;\ \ \ x \neq 3,\ x \neq 1\]
\[x^{2} - 4x + 3 = 0\]
\[x_{1} + x_{2} = 4;\ \ \ x_{1} \cdot x_{2} = 3\]
\[x_{1} = 3,\ \ x_{2} = 1.\]
\[x^{2} - 4x + 3 = (x - 3)(x - 1)\]
\[x - a = 0\ \]
\[\ x = a.\]
\[1)\ \ a = 3;\ \ \]
\[a = 1 \Longrightarrow нет\ решения.\]
\[2)\ \ a \neq 3;\ \ a \neq 1 \Longrightarrow x = a.\]