\[\left( x - 6 + \frac{36}{x + 6} \right) \cdot \frac{x + 6}{x^{2}} =\]
\[= \frac{x^{2} - 36 + 36}{x + 6} \cdot \frac{x + 6}{x^{2}} =\]
\[= \frac{x^{2} \cdot (x + 6)}{(x + 6) \cdot x^{2}} = 1 \Longrightarrow ч.т.д.\ \ \ \ \]
\[x \neq - 6;0.\]