| $$ \begin{aligned}3x(2x-5)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}6x^2-15x\end{aligned} $$ | |
| ① | Multiply $ \color{blue}{3x} $ by $ \left( 2x-5\right) $ $$ \color{blue}{3x} \cdot \left( 2x-5\right) = 6x^2-15x $$ |