Answer
$$(-7+7i)\cdot(-10-9i)=-63i^2-7i+70$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}(-7+7i)\cdot(-10-9i)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}70+63i-70i-63i^2 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}-63i^2-7i+70\end{aligned} $$ | |
| ① | Multiply each term of $ \left( \color{blue}{-7+7i}\right) $ by each term in $ \left( -10-9i\right) $. $$ \left( \color{blue}{-7+7i}\right) \cdot \left( -10-9i\right) = 70+63i-70i-63i^2 $$ |
| ② | Combine like terms: $$ 70+ \color{blue}{63i} \color{blue}{-70i} -63i^2 = -63i^2 \color{blue}{-7i} +70 $$ |
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