Question
Answer
$$(-1-5i)\cdot(-4-i)=5i^2+21i+4$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}(-1-5i)\cdot(-4-i)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}4+i+20i+5i^2 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}5i^2+21i+4\end{aligned} $$ | |
| ① | Multiply each term of $ \left( \color{blue}{-1-5i}\right) $ by each term in $ \left( -4-i\right) $. $$ \left( \color{blue}{-1-5i}\right) \cdot \left( -4-i\right) = 4+i+20i+5i^2 $$ |
| ② | Combine like terms: $$ 4+ \color{blue}{i} + \color{blue}{20i} +5i^2 = 5i^2+ \color{blue}{21i} +4 $$ |
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