\[\sqrt{\left( x^{2} + 6x \right)^{- 1}}\]
\[Область\ определения:\]
\[\left( x^{2} + 6x \right)^{- 1} \geq 0\]
\[\frac{1}{x^{2} + 6x} \geq 0\]
\[x^{2} + 6x > 0\]
\[x(x + 6) > 0\]
\[x < - 6;x > 0.\]
\[Ответ:x < - 6;x > 0.\]