Question
Answer
$$7i\cdot3i\cdot(-8-6i)=126i+168$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}7i\cdot3i\cdot(-8-6i)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}21i^2\cdot(-8-6i) \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}-21\cdot(-8-6i) \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle3}{\textcircled {3}} } }}}168+126i \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle4}{\textcircled {4}} } }}}126i+168\end{aligned} $$ | |
| ① | $$ 7 i \cdot 3 i = 21 i^{1 + 1} = 21 i^2 $$ |
| ② | $$ 21i^2 = 21 \cdot (-1) = -21 $$ |
| ③ | Multiply $ \color{blue}{-21} $ by $ \left( -8-6i\right) $ $$ \color{blue}{-21} \cdot \left( -8-6i\right) = 168+126i $$ |
| ④ | Combine like terms: $$ 126i+168 = 126i+168 $$ |
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