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