| $$ \begin{aligned}-\sqrt{216}& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}-6\sqrt{6}\end{aligned} $$ | |
| ① | $$ - \sqrt{216} =
- \sqrt{ 6 ^2 \cdot 6 } =
- \sqrt{ 6 ^2 } \, \sqrt{ 6 } =
- 6 \sqrt{ 6 }$$ |