$$ \begin{aligned}8\sqrt{2}\cdot5\sqrt{10}& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}80\sqrt{5}\end{aligned} $$ | |
① | $$ 40 \sqrt{20} =
40 \sqrt{ 2 ^2 \cdot 5 } =
40 \sqrt{ 2 ^2 } \, \sqrt{ 5 } =
40 \cdot 2 \sqrt{ 5 } =
80 \sqrt{ 5 } $$ |