Question
Answer
$$-3i(7i-5)=15i+21$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}-3i(7i-5)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}-(21i^2-15i) \xlongequal{ } \\[1 em] & \xlongequal{ }-(-21-15i) \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}21+15i \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle3}{\textcircled {3}} } }}}15i+21\end{aligned} $$ | |
| ① | Multiply $ \color{blue}{3i} $ by $ \left( 7i-5\right) $ $$ \color{blue}{3i} \cdot \left( 7i-5\right) = 21i^2-15i $$ |
| ② | Remove the parentheses by changing the sign of each term within them. $$ - \left(-21-15i \right) = 21+15i $$ |
| ③ | Combine like terms: $$ 15i+21 = 15i+21 $$ |
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