دامنه تابع $f\left( x \right)=\left\{ \begin{matrix} {{x}^{2}}-1\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,x\lt 0 \\ -{{x}^{2}}+1\,\,\,\,\,\,\,\,\,\,\,\,\,0\le x \\\end{matrix} \right.$ کدام است؟
1 )
$x\ge 0$
2 )
$x\lt 0$
$\left( -\infty ,+\infty \right)$
4 )
$x\gt0$