| $$ \begin{aligned}5x^3-9x^2+7+12x^3+7x-2& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}17x^3-9x^2+7x+5\end{aligned} $$ | |
| ① | Combine like terms: $$ \color{blue}{5x^3} -9x^2+ \color{red}{7} + \color{blue}{12x^3} +7x \color{red}{-2} = \color{blue}{17x^3} -9x^2+7x+ \color{red}{5} $$ |