Question
Answer
$$(4-5i)\cdot(-1-7i)=35i^2-23i-4$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}(4-5i)\cdot(-1-7i)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}-4-28i+5i+35i^2 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}35i^2-23i-4\end{aligned} $$ | |
| ① | Multiply each term of $ \left( \color{blue}{4-5i}\right) $ by each term in $ \left( -1-7i\right) $. $$ \left( \color{blue}{4-5i}\right) \cdot \left( -1-7i\right) = -4-28i+5i+35i^2 $$ |
| ② | Combine like terms: $$ -4 \color{blue}{-28i} + \color{blue}{5i} +35i^2 = 35i^2 \color{blue}{-23i} -4 $$ |
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