| $$ \begin{aligned}6\cdot3\sqrt{28}& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}36\sqrt{7}\end{aligned} $$ | |
| ① | $$ 18 \sqrt{28} =
18 \sqrt{ 2 ^2 \cdot 7 } =
18 \sqrt{ 2 ^2 } \, \sqrt{ 7 } =
18 \cdot 2 \sqrt{ 7 } =
36 \sqrt{ 7 } $$ |