Tap the blue circles to see an explanation.
| $$ \begin{aligned}6i\cdot(4-20i)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}24i-120i^2 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}24i+120\end{aligned} $$ | |
| ① | Multiply $ \color{blue}{6i} $ by $ \left( 4-20i\right) $ $$ \color{blue}{6i} \cdot \left( 4-20i\right) = 24i-120i^2 $$ |
| ② | $$ -120i^2 = -120 \cdot (-1) = 120 $$ |