If $x_1=2\tan^{-1}\big(\large\frac{1+x}{1-x}\big)$$,x_2=\sin^{-1}\big[\large\frac{1-x^2}{1+x^2}\big]$ where $x\in(0,1)$ then $x_1+x_2$ is equal to

Question

$(a)\;0\qquad(b)\;2\pi\qquad(c)\;\pi\qquad(d)\;4\pi$