Tap the blue circles to see an explanation.
$$ \begin{aligned}8i^3\cdot9i& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}72i^4 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}72\end{aligned} $$ | |
① | $$ 8 i^3 \cdot 9 i = 72 i^{3 + 1} = 72 i^4 $$ |
② | $$ 72i^4 = 72 \cdot i^2 \cdot i^2 =
72 \cdot ( - 1) \cdot ( - 1) =
72 $$ |