A D993: Real number $x \in \mathbb{R}$ is a principal square root for $y$ if and only if
(1) | \begin{equation} y = x^2 \end{equation} |
(2) | \begin{equation} x \geq 0 \end{equation} |
(1) | \begin{equation} y = x^2 \end{equation} |
(2) | \begin{equation} x \geq 0 \end{equation} |