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