Categories > trigonometry > Trigonometric ratios of multiple and sub-multiple angles > If $\cos (\theta -\alpha ),\ \cos \theta $and $\cos (\theta +\alpha )$are in H.P., then $\cos \theta \sec \frac{\alpha }{2}$is equal to

trigonometry

Question: If $\cos (\theta -\alpha ),\ \cos \theta $and $\cos (\theta +\alpha )$are in H.P., then $\cos \theta \sec \frac{\alpha }{2}$is equal to


1) $\pm \sqrt{2}$
2) $\pm \sqrt{3}$
3) $\pm 1/\sqrt{2}$
4) None of these
Solution: Explanation: No Solution
Trigonometric ratios of multiple and sub-multiple angles

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