Question
Answer
$$(-5+4i)\cdot(3+i)=4i^2+7i-15$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}(-5+4i)\cdot(3+i)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}-15-5i+12i+4i^2 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}4i^2+7i-15\end{aligned} $$ | |
| ① | Multiply each term of $ \left( \color{blue}{-5+4i}\right) $ by each term in $ \left( 3+i\right) $. $$ \left( \color{blue}{-5+4i}\right) \cdot \left( 3+i\right) = -15-5i+12i+4i^2 $$ |
| ② | Combine like terms: $$ -15 \color{blue}{-5i} + \color{blue}{12i} +4i^2 = 4i^2+ \color{blue}{7i} -15 $$ |
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