$\left\{\begin{matrix}\\x=\sqrt{1-y^{2}}-1\text{; }x=-\sqrt{1-y^{2}}-1\text{, }&\text{unconditionally}\\x\in \mathrm{C}\text{, }&y=0\end{matrix}\right.$

$y=i\sqrt{x}\sqrt{x+2}$
$y=0$
$y=-i\sqrt{x}\sqrt{x+2}$

$\left\{\begin{matrix}x=\sqrt{1-y^{2}}-1\text{; }x=-\sqrt{1-y^{2}}-1\text{, }&|y|\leq 1\\x\in \mathrm{R}\text{, }&y=0\end{matrix}\right.$

$\left\{\begin{matrix}\\y=0\text{, }&\text{unconditionally}\\y=\sqrt{-x\left(x+2\right)}\text{; }y=-\sqrt{-x\left(x+2\right)}\text{, }&x\geq -2\text{ and }x\leq 0\end{matrix}\right.$