Answer
$$(-5i)\cdot2i\cdot(1+7i)=70i+10$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}(-5i)\cdot2i\cdot(1+7i)& \xlongequal{ }-10i^2\cdot(1+7i) \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}10\cdot(1+7i) \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}10+70i \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle3}{\textcircled {3}} } }}}70i+10\end{aligned} $$ | |
| ① | $$ -10i^2 = -10 \cdot (-1) = 10 $$ |
| ② | Multiply $ \color{blue}{10} $ by $ \left( 1+7i\right) $ $$ \color{blue}{10} \cdot \left( 1+7i\right) = 10+70i $$ |
| ③ | Combine like terms: $$ 70i+10 = 70i+10 $$ |
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