Application Of Derivatives

Let \(\mathrm{g}(x)=f(x)+f(1-x)\) and \(f^{\prime \prime}(x) > 0, x \in(0,1)\). If \(\mathrm{g}\) is decreasing in the interval \((0, a)\) and increasing in the interval \((\alpha, 1)\), then \(\tan ^{-1}(2 \alpha)+\tan ^{-1}\left(\frac{1}{\alpha}\right)+\tan ^{-1}\left(\frac{\alpha+1}{\alpha}\right)\) is equal to :