$\operatorname{sech}^{-1}\left(\frac{1}{\sqrt{2}}\right)+\operatorname{cosech}^{-1}(-1)=$

$\operatorname{sech}^{-1}\left(\frac{1}{\sqrt{2}}\right)+\operatorname{cosech}^{-1}(-1)=$
  1. 0
  2. $\sqrt{2}+1$
  3. $\sqrt{2}$
  4. $\sqrt{2}-1$

Solution

We have, $\begin{aligned} & \operatorname{sech}^{-1}\left(\frac{1}{\sqrt{2}}\right)+\operatorname{cosec} h^{-1}(-1) \\ & =\log _e\left(\frac{1+\sqrt{1-1 / 2}}{\frac{1}{\sqrt{2}}}\right)+\log _e\left(\frac{1-\sqrt{1+1}}{-1}\right) \\ & =\log _e\left(\frac{\sqrt{2}+1}{\frac{1}{\sqrt{2}}}\right)+\log _e(\sqrt{2}-1) \\ & =\log _e(\sqrt{2}+1)+\log _e(\sqrt{2}-1) \\ & =\log _e[(\sqrt{2}+1)(\sqrt{2}-1)] \\ \end{aligned}$ $\begin{aligned} & \quad[\because \log m+\log n=\log (m \times n)] \\ & =\log _e\left((\sqrt{2})^2-1\right)=\log _e(2-1)=\log _e 1 \\ & \therefore \quad \sec h^{-1}\left(\frac{1}{\sqrt{2}}\right)+\operatorname{cosec}^{-1}(-1)=0\end{aligned}$

Asked in: AP EAMCET 2017 (26 Apr Shift 1)

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