| $$ \begin{aligned}(-i)(-3x)^2& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}(-i)\cdot9x^2 \xlongequal{ } \\[1 em] & \xlongequal{ }-9ix^2\end{aligned} $$ | |
| ① | $$ \left( -3x \right)^2 = (-3)^2x^2 = 9x^2 $$ |