Answer
$$(7+9i)\cdot(7+4i)=36i^2+91i+49$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}(7+9i)\cdot(7+4i)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}49+28i+63i+36i^2 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}36i^2+91i+49\end{aligned} $$ | |
| ① | Multiply each term of $ \left( \color{blue}{7+9i}\right) $ by each term in $ \left( 7+4i\right) $. $$ \left( \color{blue}{7+9i}\right) \cdot \left( 7+4i\right) = 49+28i+63i+36i^2 $$ |
| ② | Combine like terms: $$ 49+ \color{blue}{28i} + \color{blue}{63i} +36i^2 = 36i^2+ \color{blue}{91i} +49 $$ |
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