Tap the blue circles to see an explanation.
| $$ \begin{aligned}15i\cdot4i& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}60i^2 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}-60\end{aligned} $$ | |
| ① | $$ 15 i \cdot 4 i = 60 i^{1 + 1} = 60 i^2 $$ |
| ② | $$ 60i^2 = 60 \cdot (-1) = -60 $$ |