Question
Answer
$$(7+5i)(2i-1)=10i^2+9i-7$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}(7+5i)(2i-1)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}14i-7+10i^2-5i \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}10i^2+9i-7\end{aligned} $$ | |
| ① | Multiply each term of $ \left( \color{blue}{7+5i}\right) $ by each term in $ \left( 2i-1\right) $. $$ \left( \color{blue}{7+5i}\right) \cdot \left( 2i-1\right) = 14i-7+10i^2-5i $$ |
| ② | Combine like terms: $$ \color{blue}{14i} -7+10i^2 \color{blue}{-5i} = 10i^2+ \color{blue}{9i} -7 $$ |
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