2. Given $y=\arcsin \frac{1-x}{1+x}$, find $y^{\prime}$.

 untranslated text remains the same as requested.
\[
\begin{aligned} 2 \cdot y^{\prime} & =\frac{1}{\sqrt{1-\left(\frac{1-x}{1+x}\right)^{2}}} \cdot \frac{-(1+x)-(1-x)}{(1+x)^{2}} \\ & =-\frac{\sqrt{x}}{x(1+x)}\end{aligned}
\]