If $\theta=\tan ^{-1}\left(\frac{1}{3}\right)+\tan ^{-1}\left(\frac{1}{7}\right)+\tan ^{-1}\left(\frac{1}{13}\right) +\tan ^{-1}\left(\frac{1}{21}\right)+\tan ^{-1}\left(\frac{1}{31}\right)$, then $\tan \theta=$

If $\tan ^{-1} x=\cot h^{-1} y=\log \sqrt{5}$, then $\tan ^{-1}(x y)=$

If $f(x)=2+\left|\sin ^{-1} x\right|$ and $A=\left\{x \in R / f^1(x)\right.$ exists $\}$, then $A=$

The equation $\cos ^{-1}(1-x)-2 \cos ^{-1} x=\frac{\pi}{2}$ has