\[\ x^{2} = 10\]
\[x = \pm \sqrt{10}\]
\[Ответ:\ \ \ \ x = \pm \sqrt{10}.\]
\[\ x \geq 0:\ \]
\[x^{2}\sqrt{9x^{2}} = x^{2} \cdot 3|x| = 3x^{3}.\]