| $$ \begin{aligned}2x(x^2+3x)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}2x^3+6x^2\end{aligned} $$ | |
| ① | Multiply $ \color{blue}{2x} $ by $ \left( x^2+3x\right) $ $$ \color{blue}{2x} \cdot \left( x^2+3x\right) = 2x^3+6x^2 $$ |