Question
Answer
$$(7i-1)\cdot(-8-9i)=-63i^2-47i+8$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}(7i-1)\cdot(-8-9i)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}-56i-63i^2+8+9i \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}-63i^2-47i+8\end{aligned} $$ | |
| ① | Multiply each term of $ \left( \color{blue}{7i-1}\right) $ by each term in $ \left( -8-9i\right) $. $$ \left( \color{blue}{7i-1}\right) \cdot \left( -8-9i\right) = -56i-63i^2+8+9i $$ |
| ② | Combine like terms: $$ \color{blue}{-56i} -63i^2+8+ \color{blue}{9i} = -63i^2 \color{blue}{-47i} +8 $$ |
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