Complex division

$i^{-1} = \frac{1}{i}$ . Extend with $i$ gives $\frac {1 \times i} {i × i} = \frac {i}{-1} = -i$

Remember that $\sqrt{a} \times \sqrt{b}$ is only equal to $\sqrt{a \times b}$ , when $a,b$ is bigger or equal to $0$ .