| $$ \begin{aligned}c^2(-c^2+2c-3)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}-c^4+2c^3-3c^2\end{aligned} $$ | |
| ① | Multiply $ \color{blue}{c^2} $ by $ \left( -c^2+2c-3\right) $ $$ \color{blue}{c^2} \cdot \left( -c^2+2c-3\right) = -c^4+2c^3-3c^2 $$ |