| $$ \begin{aligned}2\cdot10 \cdot \frac{\sqrt{3}}{3}& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}\frac{20\sqrt{3}}{3}\end{aligned} $$ | |
| ① | $$ \color{blue}{ 2 } \cdot 10 \sqrt{3} = 20 \sqrt{3} $$$$ \color{blue}{ 1 } \cdot 3 = 3 $$ |