Question
Answer
$$(5+2i)\cdot(-3+9i)=18i^2+39i-15$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}(5+2i)\cdot(-3+9i)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}-15+45i-6i+18i^2 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}18i^2+39i-15\end{aligned} $$ | |
| ① | Multiply each term of $ \left( \color{blue}{5+2i}\right) $ by each term in $ \left( -3+9i\right) $. $$ \left( \color{blue}{5+2i}\right) \cdot \left( -3+9i\right) = -15+45i-6i+18i^2 $$ |
| ② | Combine like terms: $$ -15+ \color{blue}{45i} \color{blue}{-6i} +18i^2 = 18i^2+ \color{blue}{39i} -15 $$ |
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