| $$ \begin{aligned}3\cdot10\sqrt{40}& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}60\sqrt{10}\end{aligned} $$ | |
| ① | $$ 30 \sqrt{40} =
30 \sqrt{ 2 ^2 \cdot 10 } =
30 \sqrt{ 2 ^2 } \, \sqrt{ 10 } =
30 \cdot 2 \sqrt{ 10 } =
60 \sqrt{ 10 } $$ |