| $$ \begin{aligned}2c^6(10c^8+3c)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}20c^{14}+6c^7\end{aligned} $$ | |
| ① | Multiply $ \color{blue}{2c^6} $ by $ \left( 10c^8+3c\right) $ $$ \color{blue}{2c^6} \cdot \left( 10c^8+3c\right) = 20c^{14}+6c^7 $$ |