\[\frac{x^{2}}{x - 4} + \frac{2x}{4 - x} = \frac{8}{x - 4}\]
\[\frac{x^{2}}{x - 4} - \frac{2x}{x - 4} - \frac{8}{x - 4} = 0\]
\[\frac{x^{2} - 2x - 8}{x - 4} = 0\ \ \ \ \ \ \ \ \ \ \ x \neq 4\]
\[x^{2} - 2x - 8 = 0\]
\[D = ( - 2)^{2} - 4 \cdot 1 \cdot ( - 8) =\]
\[= + 32 = 36\]
\[x_{1} = \frac{2 + \sqrt{36}}{2} = \frac{2 + 6}{2} = \frac{8}{2} =\]
\[= 4\ \ (не\ подходит)\]
\[x_{2} = \frac{2 - \sqrt{36}}{2} = \frac{2 - 6}{2} = \frac{- 4}{2} =\]
\[= - 2.\]
\[Ответ: - 2.\]