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If \(\sec\theta+\text{cosec}\theta = a\) and \(\tan\theta+\cot\theta = b\), find the value of \(\text{cosec}\,2\theta\).

This question was previously asked in
RRB NTPC 2025 Under Graduate CBT 2 Question Paper PDF (17-Sep-2026) (Shift 1)
The correct answer is

\(\dfrac{b}{2}\)

\(\tan\theta+\cot\theta = \dfrac{\sin\theta}{\cos\theta}+\dfrac{\cos\theta}{\sin\theta} = \dfrac{1}{\sin\theta\cos\theta} = \dfrac{2}{\sin2\theta} = b\).

So \(\sin2\theta = \dfrac{2}{b}\).

\(\text{cosec}\,2\theta = \dfrac{1}{\sin2\theta} = \dfrac{b}{2}\).

Hence, the value of \(\text{cosec}\,2\theta\) is \(\tfrac{b}{2}\).

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