| $$ \begin{aligned}2x+x^4+8x^4+4x& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}9x^4+6x\end{aligned} $$ | |
| ① | Combine like terms: $$ \color{blue}{2x} + \color{red}{x^4} + \color{red}{8x^4} + \color{blue}{4x} = \color{red}{9x^4} + \color{blue}{6x} $$ |