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NTA Abhyas 2020
Exam
NTA Abhyas
Year
2020
Subject
Mathematics
Chapter
Hyperbola

NTA Abhyas 2020 · Mathematics · Hyperbola

If the eccentricity of the hyperbola x^ 2 (1 + sin θ) ^ 2 - y^ 2 ^...

If the eccentricity of the hyperbola x2(1+sinθ)2−y2cos⁡2θ=1\dfrac{x^{2}}{{\left(1 + sin \theta\right)}^{2}} - \dfrac{y^{2}}{\cos^{2} \theta} = 1 is 23,\dfrac{2}{\sqrt{3}}, then the sum of all the possible values of θ\theta is (where, θ∈(0,π))\theta \in \left(0, \pi\right))

Options

  1. A5π4\dfrac{5\pi}{4}
  2. B2π3\dfrac{2\pi}{3}
  3. C7π4\dfrac{7\pi}{4}
  4. Dπ\pi

Correct answer

D. π\pi

Step-by-step solution

e2=1+cos⁡2θ(1+sinθ)2=43⇒cos⁡2θ(1+sinθ)2=13e^{2} = 1 + \dfrac{\cos^{2} \theta}{\left(1 + sin \theta\right)2} = \dfrac{4}{3} ⇒ \dfrac{\cos^{2} \theta}{\left(1 + sin \theta\right)2} = \dfrac{1}{3}
⇒[cosθ1+sinθ]2=13⇒[sin⁡(π2−θ)1+cos⁡(π2−θ)]2=13⇒ \left[\dfrac{cos \theta}{1 + sin \theta}\right]2 = \dfrac{1}{3} ⇒ \left[\dfrac{\sin \left(\dfrac{\pi}{2} - \theta\right)}{1 + \cos \left(\dfrac{\pi}{2} - \theta\right)}\right]2 = \dfrac{1}{3}
⇒tan⁡2(π4−θ2)=13⇒ \tan^{2} \left(\dfrac{\pi}{4} - \dfrac{\theta}{2}\right) = \dfrac{1}{3}
π4−θ2=−π6,π6⇒θ2=π4−π6,π4+π6\dfrac{\pi}{4} - \dfrac{θ}{2} = \dfrac{- \pi}{6}, \dfrac{\pi}{6} ⇒ \dfrac{θ}{2} = \dfrac{\pi}{4} - \dfrac{\pi}{6}, \dfrac{\pi}{4} + \dfrac{\pi}{6}
θ=π2±π3=π6,5π6\theta = \dfrac{\pi}{2} \pm \dfrac{\pi}{3} = \dfrac{\pi}{6}, \dfrac{5\pi}{6}

Hence, the required sum =π= \pi

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