| $$ \begin{aligned}\sqrt{5}\cdot(\sqrt{5}-\sqrt{2})& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}5-\sqrt{10}\end{aligned} $$ | |
| ① | $$ \color{blue}{ \sqrt{5} } \cdot \left( \sqrt{5}- \sqrt{2}\right) = \color{blue}{ \sqrt{5}} \cdot \sqrt{5}+\color{blue}{ \sqrt{5}} \cdot- \sqrt{2} = \\ = 5- \sqrt{10} $$ |