Question
Answer
$$(-4-5i)\cdot(7+9i)=-45i^2-71i-28$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}(-4-5i)\cdot(7+9i)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}-28-36i-35i-45i^2 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}-45i^2-71i-28\end{aligned} $$ | |
| ① | Multiply each term of $ \left( \color{blue}{-4-5i}\right) $ by each term in $ \left( 7+9i\right) $. $$ \left( \color{blue}{-4-5i}\right) \cdot \left( 7+9i\right) = -28-36i-35i-45i^2 $$ |
| ② | Combine like terms: $$ -28 \color{blue}{-36i} \color{blue}{-35i} -45i^2 = -45i^2 \color{blue}{-71i} -28 $$ |
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