$\begin{align}
& y=\left\{ \begin{matrix}
{{x}^{\frac{1}{2}}}+1\,\,\,\,\,,\,\,\,x \gt 0 \\
-{{(-x)}^{\frac{1}{2}}}+1\,\,\,\,\,,\,\,\,\,x \lt 0 \\
\end{matrix} \right. \\
& ya \\
& y=\left\{ \begin{matrix}
\sqrt{x}+1\,\,\,\,,\,\,\,\,x \gt 0 \\
-\sqrt{-x}+1\,\,\,\,\,,\,\,\,x \lt 0 \\
\end{matrix} \right. \\
& \Rightarrow {y}'=\left\{ \begin{matrix}
\frac{1}{2}{{x}^{\frac{1}{2}}}\,\,\,\,,\,\,\,\,x \gt 0 \\
\frac{1}{2}{{(-x)}^{\frac{1}{2}}}\,\,\,\,,\,\,\,\,\,x \lt 0 \\
\end{matrix} \right.\,\,\,\,\,\,\,\Rightarrow {y}''=\left\{ \begin{matrix}
-\frac{1}{4}{{x}^{-\frac{3}{2}}}\,\,\,\,,\,\,\,\,x \gt 0 \\
\frac{1}{4}{{(-x)}^{-\frac{3}{2}}}\,\,\,\,\,,\,\,\,\,x \lt 0 \\
\end{matrix} \right. \\
& \Rightarrow {y}''=\left\{ \begin{matrix}
-\frac{1}{4}.\frac{1}{x\sqrt{x}}\,\,\,\,,\,\,\,x \gt 0 \\
\frac{1}{4}.\frac{1}{-x\sqrt{-x}}\,\,\,\,,\,\,\,x \lt 0 \\
\end{matrix} \right. \\
\end{align}$
به ازای $x \gt 0$ تقعر رو به پایین و به ازای $x \lt 0$ تقعر رو به بالا است. بنابراین بازهٔ موردنظر $(-\infty ,0)$ است.