| $$ \begin{aligned}4i(-3i)& \xlongequal{ }-12i^2 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}12\end{aligned} $$ | |
| ① | $$ -12i^2 = -12 \cdot (-1) = 12 $$ |