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JEE Main 20178 AprilOnline
Exam
JEE Main
Year
2017
Date
8 April
Mode
Online
Subject
Mathematics
Chapter
Inverse Trigonometric Functions

JEE Main 2017 · 8 April · Online · Mathematics · Inverse Trigonometric Functions

The value of ^ - 1 [ 1 + x ^ 2 + 1 - x ^ 2 1 + x ^ 2 - 1 - x ^ 2 ],...

The value of tan⁡−1[1+x2+1−x21+x2−1−x2],∣x∣<12,x≠0,\tan^{- 1} \left[\dfrac{\sqrt{1 + {x}^{2}} + \sqrt{1 - {x}^{2}}}{\sqrt{1 + {x}^{2}} - \sqrt{1 - {x}^{2}}}\right], \left|x\right| < \dfrac{1}{2}, x \ne 0, is equal to:

Options

  1. Aπ4+12cos⁡−1x2\dfrac{\pi}{4} + \dfrac{1}{2}\cos^{- 1} {x}^{2}
  2. Bπ4−cos⁡−1x2\dfrac{\pi}{4} - \cos^{- 1} {x}^{2}
  3. Cπ4−12cos⁡−1x2\dfrac{\pi}{4} - \dfrac{1}{2}\cos^{- 1} {x}^{2}
  4. Dπ4+cos⁡−1x2\dfrac{\pi}{4} + \cos^{- 1} {x}^{2}

Correct answer

A. π4+12cos⁡−1x2\dfrac{\pi}{4} + \dfrac{1}{2}\cos^{- 1} {x}^{2}

Step-by-step solution

Assume that ,
x2=cos⁡2θ;θ=12cos⁡−1x2{x}^{2} = \cos 2\theta; \theta = \dfrac{1}{2}\cos^{-1}{x}^{2}

∴tan⁡−1[1+cos⁡2θ+1−cos⁡2θ1+cos⁡2θ−1−cos⁡2θ]=tan⁡−1[2cos⁡2θ+2sin⁡2θ2cos⁡2θ−2sin⁡2θ]=tan⁡−1[cosθ+sinθcosθ−sinθ]∴ \tan^{- 1} \left[\dfrac{\sqrt{1 + \cos 2\theta} + \sqrt{1 - \cos 2\theta}}{\sqrt{1 + \cos 2\theta} - \sqrt{1 - \cos 2\theta}}\right] = \tan^{- 1} \left[\dfrac{\sqrt{2\cos^{2}\theta} + \sqrt{2\sin^{2}\theta}}{\sqrt{2\cos^{2}\theta} - \sqrt{2\sin^{2}\theta}}\right] = \tan^{- 1} \left[\dfrac{cos\theta + sin\theta}{cos\theta - sin\theta}\right]
=tan⁡−1[1+tanθ1−tanθ]= \tan^{- 1} \left[\dfrac{1 + tan \theta}{1 - tan \theta}\right]

=tan⁡−1[tan⁡(π4+θ)]= \tan^{- 1} \left[\tan \left(\dfrac{\pi}{4} + \theta\right)\right]

=π4+12cos⁡−1x2= \dfrac{\pi}{4} + \dfrac{1}{2}\cos^{- 1} {x}^{2}
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