Tap the blue circles to see an explanation.
$$ \begin{aligned}(3ix+9)(ix-3)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}3i^2x^2-9ix+9ix-27 \xlongequal{ } \\[1 em] & \xlongequal{ }3i^2x^2 -\cancel{9ix}+ \cancel{9ix}-27 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}3i^2x^2-27\end{aligned} $$ | |
① | Multiply each term of $ \left( \color{blue}{3ix+9}\right) $ by each term in $ \left( ix-3\right) $. $$ \left( \color{blue}{3ix+9}\right) \cdot \left( ix-3\right) = 3i^2x^2 -\cancel{9ix}+ \cancel{9ix}-27 $$ |
② | Combine like terms: $$ 3i^2x^2 \, \color{blue}{ -\cancel{9ix}} \,+ \, \color{blue}{ \cancel{9ix}} \,-27 = 3i^2x^2-27 $$ |