Question
Answer
$$(6-3i)\cdot(6+3i)=-9i^2+36$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}(6-3i)\cdot(6+3i)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}36+18i-18i-9i^2 \xlongequal{ } \\[1 em] & \xlongequal{ }36+ \cancel{18i} -\cancel{18i}-9i^2 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}-9i^2+36\end{aligned} $$ | |
| ① | Multiply each term of $ \left( \color{blue}{6-3i}\right) $ by each term in $ \left( 6+3i\right) $. $$ \left( \color{blue}{6-3i}\right) \cdot \left( 6+3i\right) = 36+ \cancel{18i} -\cancel{18i}-9i^2 $$ |
| ② | Combine like terms: $$ 36+ \, \color{blue}{ \cancel{18i}} \, \, \color{blue}{ -\cancel{18i}} \,-9i^2 = -9i^2+36 $$ |
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