Question
Answer
$$(2-7i)\cdot(-10-10i)=70i^2+50i-20$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}(2-7i)\cdot(-10-10i)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}-20-20i+70i+70i^2 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}70i^2+50i-20\end{aligned} $$ | |
| ① | Multiply each term of $ \left( \color{blue}{2-7i}\right) $ by each term in $ \left( -10-10i\right) $. $$ \left( \color{blue}{2-7i}\right) \cdot \left( -10-10i\right) = -20-20i+70i+70i^2 $$ |
| ② | Combine like terms: $$ -20 \color{blue}{-20i} + \color{blue}{70i} +70i^2 = 70i^2+ \color{blue}{50i} -20 $$ |
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