Let $S = \left\{ x \in R : 0 < x < 1 \text{ and } 2\tan^{-1}\left(\frac{1-x}{1+x}\right) = \cos^{-1}\left(\frac{1-x^2}{1+x^2}\right) \right\}$. If $n(S)$ denotes the number of elements in $S$ then:
\( n(S)=0 \)
\( n(S)=1 \) and the element in \( S \) is less than \( \frac{1}{2} \)
\( n(S)=1 \) and the element in \( S \) is more than \( \frac{1}{2} \)
\( n(S)=2 \) and only one element in \( S \) is less than \( \frac{1}{2} \)