| $$ \begin{aligned}9x^3y^4(3x^3-5y)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}27x^6y^4-45x^3y^5\end{aligned} $$ | |
| ① | Multiply $ \color{blue}{9x^3y^4} $ by $ \left( 3x^3-5y\right) $ $$ \color{blue}{9x^3y^4} \cdot \left( 3x^3-5y\right) = 27x^6y^4-45x^3y^5 $$ |