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JEE Main 201912 AprilMorning Shift
Exam
JEE Main
Year
2019
Date
12 April
Shift
Morning Shift
Subject
Mathematics
Chapter
Functions

JEE Main 2019 · 12 April · Morning Shift · Mathematics · Functions

For xϵ ( 0, (3)/(2) ) , let f(x) = x , g(x) = x and h(x) = 1 - x ^...

For xϵ(0,32),xϵ ( 0, \dfrac{3}{2} ) , let f(x)=x,g(x)=tan⁡xf\left(x\right) = \sqrt{x}, g\left(x\right) = \tan x and h(x)=1−x21+x2h\left(x\right) = \dfrac{1 - {x}^{2}}{1 + {x}^{2}} . If ϕ(x)=(hof)og)(x),ϕ\left(x\right) = ( hof ) og ) ( x ) , then ϕ(π3)ϕ\left(\dfrac{\pi}{3}\right) is equal to:

Options

  1. Atanπ12tan \dfrac{\pi}{12}
  2. Btan5π12tan \dfrac{5\pi}{12}
  3. Ctan7π12tan \dfrac{7\pi}{12}
  4. Dtan11π12tan \dfrac{11\pi}{12}

Correct answer

D. tan11π12tan \dfrac{11\pi}{12}

Step-by-step solution

f(x)=xf\left(x\right) = \sqrt{x}

g(x)=tan⁡xg\left(x\right) = \tan x

h(x)=1−x21+x2h\left(x\right) = \dfrac{1 - {x}^{2}}{1 + {x}^{2}}
fog(x)=tan⁡xfog\left(x\right) = \sqrt{\tan x}
hofog(x)=h(tan⁡x)hofog\left(x\right) = h\left(\sqrt{\tan x}\right)

=1−tan⁡x1+tan⁡x=tan⁡(π4−x)= \dfrac{1 - \tan x}{1 + \tan x} = \tan \left(\dfrac{\pi}{4} - x\right)
ϕ(x)=tan⁡(π4−x)ϕ\left(x\right) = \tan \left(\dfrac{\pi}{4} - x\right)
ϕ(π3)=tan⁡(π4−π3)ϕ\left(\dfrac{\pi}{3}\right) = \tan \left(\dfrac{\pi}{4} - \dfrac{\pi}{3}\right)

=tan⁡(−π12)=−tanπ12= \tan \left(- \dfrac{\pi}{12}\right) = - tan\dfrac{\pi}{12}

=tan⁡(π−π12)=tan11π12= \tan \left(\pi - \dfrac{\pi}{12}\right) = tan\dfrac{11\pi}{12}

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