If $\sec \theta \cosh y=\operatorname{cosec} x$ and $\operatorname{cosec} \theta \sinh y=\sec x$, then…

If $\sec \theta \cosh y=\operatorname{cosec} x$ and $\operatorname{cosec} \theta \sinh y=\sec x$, then $\sinh ^2 y=$
  1. $\cos ^2 x$
  2. $\cos x$
  3. $\sin ^2 x$
  4. $\sin x$

Solution

Since, $\sec \theta \cosh y=\operatorname{cosec} x$ and $\operatorname{cosec} \theta \sinh y=\sec x$
If we square and add Eqs. (i) and (ii), $ \begin{array}{cc} \Rightarrow & 1=\sin ^2 x \cosh ^2 y+\cos ^2 x \sinh ^2 y \\ \Rightarrow & \sin ^2 x\left(1+\sinh ^2 y\right)+\cos ^2 x \sinh ^2 y=1 \\ \Rightarrow & \sinh ^2 y+\sin ^2 x=1 \\ \Rightarrow & \sinh ^2 y=1-\sin ^2 x=\cos ^2 x \end{array} $

Asked in: AP EAMCET 2018 (22 Apr Shift 2)

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