Question
Answer
$$(7+i)\cdot(6-9i)=-9i^2-57i+42$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}(7+i)\cdot(6-9i)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}42-63i+6i-9i^2 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}-9i^2-57i+42\end{aligned} $$ | |
| ① | Multiply each term of $ \left( \color{blue}{7+i}\right) $ by each term in $ \left( 6-9i\right) $. $$ \left( \color{blue}{7+i}\right) \cdot \left( 6-9i\right) = 42-63i+6i-9i^2 $$ |
| ② | Combine like terms: $$ 42 \color{blue}{-63i} + \color{blue}{6i} -9i^2 = -9i^2 \color{blue}{-57i} +42 $$ |
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