If $ \sin ^{-1} x +\cos ^{-1} \bigg(\large\frac{1}{2}=\frac{\pi}{2} $ then x is

Question

$\begin{array}{1 1} 0 \\ \large\frac{1}{\sqrt 5} \\\large\frac{2}{\sqrt 5} \\\large\frac{\sqrt 3}{2} \end{array} $