Tap the blue circles to see an explanation.
| $$ \begin{aligned}-12i^{15}+i^{23}& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}12i-i\end{aligned} $$ | |
| ① | $$ -12i^{15} = -12 \cdot i^{4 \cdot 3 + 3} =
-12 \cdot \left( i^4 \right)^{ 3 } \cdot i^3 =
-12 \cdot 1^{ 3 } \cdot (-i) =
-12 \cdot -i = 12i $$ |
| ② | $$ i^{23} = i^{4 \cdot 5 + 3} =
\left( i^4 \right)^{ 5 } \cdot i^3 =
1^{ 5 } \cdot (-i) =
-i = -i $$ |