Tap the blue circles to see an explanation.
| $$ \begin{aligned}(3i)^2& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}9i^2 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}-9\end{aligned} $$ | |
| ① | $$ \left( 3i \right)^2 = 3^2i^2 = 9i^2 $$ |
| ② | $$ 9i^2 = 9 \cdot (-1) = -9 $$ |