$$ \begin{aligned}5s^6t^2+6st^9-8s^6t^2-6t^7& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}6st^9-3s^6t^2-6t^7\end{aligned} $$ | |
① | Combine like terms: $$ \color{blue}{5s^6t^2} +6st^9 \color{blue}{-8s^6t^2} -6t^7 = 6st^9 \color{blue}{-3s^6t^2} -6t^7 $$ |