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Inverse Trigonometric Functions question

2021 · 20 Jul · Shift 2 · Q25
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  5. /2021 · 20 Jul · Shift 2 · Q25

Inverse Trigonometric Functions question

2021 · 20 Jul · Shift 2 · Q25

JEE MainMathematicsInverse Trigonometric FunctionsMCQ+4 / −1
The value of tan⁡(2tan⁡−1(35)+sin⁡−1(513))\tan \left( {2{{\tan }^{ - 1}}\left( {{3 \over 5}} \right) + {{\sin }^{ - 1}}\left( {{5 \over {13}}} \right)} \right)tan(2tan−1(53​)+sin−1(135​)) is equal to :
  1. A
    −18169{{ - 181} \over {69}}69−181​
  2. B
    22021{{220} \over {21}}21220​
  3. C
    −29176{{ - 291} \over {76}}76−291​
  4. D
    15163{{151} \over {63}}63151​
View written solutionFree

Correct answer: B

  1. Let θ=tan⁡−1(35),ϕ=sin⁡−1(513).\theta = \tan^{-1}\left(\frac{3}{5}\right), \qquad \phi = \sin^{-1}\left(\frac{5}{13}\right).θ=tan−1(53​),ϕ=sin−1(135​).

    We need to find tan⁡(2θ+ϕ).\tan(2\theta + \phi).tan(2θ+ϕ).

  2. First compute tan⁡2θ\tan 2\thetatan2θ.

    Since tan⁡θ=35,\tan \theta = \frac{3}{5},tanθ=53​, we use tan⁡2θ=2tan⁡θ1−tan⁡2θ.\tan 2\theta = \frac{2\tan\theta}{1-\tan^2\theta}.tan2θ=1−tan2θ2tanθ​.

    Therefore,

    = \frac{\frac{6}{5}}{1-\frac{9}{25}} = \frac{\frac{6}{5}}{\frac{16}{25}} = \frac{6}{5}\cdot \frac{25}{16} = \frac{15}{8}.$$
  3. Now compute tan⁡ϕ\tan \phitanϕ.

    Given sin⁡ϕ=513.\sin \phi = \frac{5}{13}.sinϕ=135​. Since ϕ=sin⁡−1(5/13)\phi = \sin^{-1}(5/13)ϕ=sin−1(5/13) lies in the principal range [−π/2,π/2][-\pi/2,\pi/2][−π/2,π/2], and 5/13>05/13>05/13>0, we have ϕ\phiϕ in the first quadrant.

    Hence cos⁡ϕ=1−sin⁡2ϕ=1−25169=144169=1213.\cos \phi = \sqrt{1-\sin^2\phi} = \sqrt{1-\frac{25}{169}} = \sqrt{\frac{144}{169}} = \frac{12}{13}.cosϕ=1−sin2ϕ​=1−16925​​=169144​​=1312​.

    So, tan⁡ϕ=sin⁡ϕcos⁡ϕ=5/1312/13=512.\tan \phi = \frac{\sin\phi}{\cos\phi} = \frac{5/13}{12/13} = \frac{5}{12}.tanϕ=cosϕsinϕ​=12/135/13​=125​.

  4. Use the tangent addition formula: tan⁡(2θ+ϕ)=tan⁡2θ+tan⁡ϕ1−tan⁡2θtan⁡ϕ.\tan(2\theta+\phi) = \frac{\tan 2\theta + \tan \phi}{1-\tan 2\theta\tan \phi}.tan(2θ+ϕ)=1−tan2θtanϕtan2θ+tanϕ​.

    Substitute the values: tan⁡(2θ+ϕ)=158+5121−158⋅512.\tan(2\theta+\phi) = \frac{\frac{15}{8}+\frac{5}{12}}{1-\frac{15}{8}\cdot \frac{5}{12}}.tan(2θ+ϕ)=1−815​⋅125​815​+125​​.

  5. Simplify the numerator: 158+512=45+1024=5524.\frac{15}{8}+\frac{5}{12} = \frac{45+10}{24} = \frac{55}{24}.815​+125​=2445+10​=2455​.

    Simplify the denominator: 1−158⋅512=1−7596=1−2532=732.1-\frac{15}{8}\cdot\frac{5}{12} = 1-\frac{75}{96} = 1-\frac{25}{32} = \frac{7}{32}.1−815​⋅125​=1−9675​=1−3225​=327​.

  6. Therefore, tan⁡(2θ+ϕ)=55/247/32=5524⋅327=55⋅43⋅7=22021.\tan(2\theta+\phi) = \frac{55/24}{7/32} = \frac{55}{24}\cdot \frac{32}{7} = \frac{55\cdot 4}{3\cdot 7} = \frac{220}{21}.tan(2θ+ϕ)=7/3255/24​=2455​⋅732​=3⋅755⋅4​=21220​.

  7. Hence the correct option is 22021\boxed{\frac{220}{21}}21220​​ which is Option B.

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