Can you find $x$ ?

By convention, $\sqrt{x}$ is defined to be the non-negative value $y$ such that $y^2=x$ . We could just as well have defined it as the non-positive value of $y$ with this property, but it is valuable to have $\sqrt{x}$ be a function, so we must choose one or the other. Thus, by definition, $\sqrt{x}\geq 0$ for all real $x$ .

$\sqrt{x}\geq0$ if $x$ is non-negative real. $\sqrt{x}$ isn't real if $x$ is negative real. Therefore, there is no $\bf{\text{real}}$ value of $x$ when $\sqrt{x}=-1$ .