| $$ \begin{aligned}y^3+9xy^2+24x^2y+16x^3-cx^3-1& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}-cx^3+16x^3+24x^2y+9xy^2+y^3-1\end{aligned} $$ | |
| ① | Combine like terms: $$ -cx^3+16x^3+24x^2y+9xy^2+y^3-1 = -cx^3+16x^3+24x^2y+9xy^2+y^3-1 $$ |