Answer
$$4i\cdot(9-7i)=36i+28$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}4i\cdot(9-7i)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}36i-28i^2 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}36i+28\end{aligned} $$ | |
| ① | Multiply $ \color{blue}{4i} $ by $ \left( 9-7i\right) $ $$ \color{blue}{4i} \cdot \left( 9-7i\right) = 36i-28i^2 $$ |
| ② | $$ -28i^2 = -28 \cdot (-1) = 28 $$ |
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