The derivative of $\tan^{-1}\left(\frac{\sqrt{1+x^2}-1}{x}\right)$ with respect to $\tan^{-1}\left(\frac{2x\sqrt{1-x^2}}{1-2x^2}\right)$ at $x = \frac{1}{2}$ is:\\
(1) $\frac{2\sqrt{3}}{5}$\\
(2) $\frac{\sqrt{3}}{12}$\\
(3) $\frac{2\sqrt{3}}{3}$\\
(4) $\frac{\sqrt{3}}{10}$