| $$ \begin{aligned}x(x^2-5)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}x^3-5x\end{aligned} $$ | |
| ① | Multiply $ \color{blue}{x} $ by $ \left( x^2-5\right) $ $$ \color{blue}{x} \cdot \left( x^2-5\right) = x^3-5x $$ |