$2 \operatorname{coth}^{-1}(4)+\sec h^{-1}\left(\frac{3}{5}\right)=$

If $y=\sin ^{-1} x$, then $\left(1-x^2\right) y_2-x y_1=$

If $\cos ^{-1} 2 x+\cos ^{-1} 3 x=\frac{\pi}{3}$ and $4 x^2=\frac{a}{b}$, then $a+b$ is equal to

If $\theta=\sec ^{-1}(\cosh u)$, then $u=$