Question
Answer
$$(12+9i)\cdot(-9-3i)=-27i^2-117i-108$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}(12+9i)\cdot(-9-3i)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}-108-36i-81i-27i^2 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}-27i^2-117i-108\end{aligned} $$ | |
| ① | Multiply each term of $ \left( \color{blue}{12+9i}\right) $ by each term in $ \left( -9-3i\right) $. $$ \left( \color{blue}{12+9i}\right) \cdot \left( -9-3i\right) = -108-36i-81i-27i^2 $$ |
| ② | Combine like terms: $$ -108 \color{blue}{-36i} \color{blue}{-81i} -27i^2 = -27i^2 \color{blue}{-117i} -108 $$ |
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