\[\boxed{\mathbf{47.}}\]
\[\frac{x^{2} - a^{2}}{x - 4} = 0\]
\[\frac{(x - a)(x + a)}{x - 4} = 0\]
\[x - 4 \neq 0\]
\[x \neq 4.\]
\[1)\ x - a = 0\]
\[x = a.\]
\[2)\ x + a = 0\]
\[x = - a.\]
\[a = 4;a = - 4;a = 0.\]
\[Ответ:a = \pm 4;a = 0.\]