Question
Answer
$$(-9+7i)\cdot(-9-5i)=-35i^2-18i+81$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}(-9+7i)\cdot(-9-5i)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}81+45i-63i-35i^2 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}-35i^2-18i+81\end{aligned} $$ | |
| ① | Multiply each term of $ \left( \color{blue}{-9+7i}\right) $ by each term in $ \left( -9-5i\right) $. $$ \left( \color{blue}{-9+7i}\right) \cdot \left( -9-5i\right) = 81+45i-63i-35i^2 $$ |
| ② | Combine like terms: $$ 81+ \color{blue}{45i} \color{blue}{-63i} -35i^2 = -35i^2 \color{blue}{-18i} +81 $$ |
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