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Question

What is \(\tan^{2}\left(\frac{1}{2}\cos^{-1}\frac{1}{3}\right)\) equal to?

This question was previously asked in
NDA 2 2026 GAT Question Paper (13-Sep-2026)
The correct answer is

\(1/2\)

Let \(\theta = \cos^{-1}(1/3)\), so \(\cos\theta = 1/3\). Using \(\tan^{2}(\theta/2) = \dfrac{1-\cos\theta}{1+\cos\theta}\), we get \(\dfrac{1-1/3}{1+1/3} = \dfrac{2/3}{4/3} = 1/2\).

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