Answer
$$7i(-3i)=21$$
Explanation
| $$ \begin{aligned}7i(-3i)& \xlongequal{ }-21i^2 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}21\end{aligned} $$ | |
| ① | $$ -21i^2 = -21 \cdot (-1) = 21 $$ |
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