Answer
$$5i+7ii=5i-7$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}5i+7ii& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}5i+7i^2 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}5i-7\end{aligned} $$ | |
| ① | $$ 7 i i = 7 i^{1 + 1} = 7 i^2 $$ |
| ② | $$ 7i^2 = 7 \cdot (-1) = -7 $$ |
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