| $$ \begin{aligned}63a^3b^7-81a^6b^8+36a^5b^4& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}-81a^6b^8+63a^3b^7+36a^5b^4\end{aligned} $$ | |
| ① | Combine like terms: $$ -81a^6b^8+63a^3b^7+36a^5b^4 = -81a^6b^8+63a^3b^7+36a^5b^4 $$ |