Question
Answer
$$-5i(4i-9)=45i+20$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}-5i(4i-9)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}-(20i^2-45i) \xlongequal{ } \\[1 em] & \xlongequal{ }-(-20-45i) \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}20+45i \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle3}{\textcircled {3}} } }}}45i+20\end{aligned} $$ | |
| ① | Multiply $ \color{blue}{5i} $ by $ \left( 4i-9\right) $ $$ \color{blue}{5i} \cdot \left( 4i-9\right) = 20i^2-45i $$ |
| ② | Remove the parentheses by changing the sign of each term within them. $$ - \left(-20-45i \right) = 20+45i $$ |
| ③ | Combine like terms: $$ 45i+20 = 45i+20 $$ |
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