JEE Main & Advanced JEE Main Paper (Held on 12-4-2019 Morning)

  • question_answer
    For\[x\in \left( 0,\frac{3}{2} \right),let\,f(x)=\sqrt{x},g(x)=tanx\]and\[h(x)=\frac{1-{{x}^{2}}}{1+{{x}^{2}}}.\]If \[\phi (x)=((h\,of)og)(x),\]then\[\phi =\left( \frac{\pi }{3} \right)\]is equal to: [JEE Main Held on 12-4-2019 Morning]

    A) \[\tan \frac{\pi }{12}\]            

    B) \[\tan \frac{7\pi }{12}\]

    C) \[\tan \frac{11\pi }{12}\]        

    D) \[\tan \frac{5\pi }{12}\]

    Correct Answer: C

    Solution :

                \[f(x)=\sqrt{x},g(x)=tanx,\,h(x)=\frac{1-{{x}^{2}}}{1+{{x}^{2}}}\]           \[fog(x)=\sqrt{\tan x}\]           \[hofog(x)=h(\sqrt{\tan x})=\frac{1-\tan x}{1+\tan x}\]           \[=-\tan \left( \frac{\pi }{4}-x \right)\]           \[\phi (x)=\tan \left( \frac{\pi }{4}-x \right)\]           \[\phi \left( \frac{\pi }{3} \right)=\tan \left( \frac{\pi }{4}-\frac{\pi }{3} \right)=\tan \left( -\frac{\pi }{12} \right)=-\tan \frac{\pi }{12}\]           \[=\tan \left( \pi -\frac{\pi }{12} \right)=\tan \frac{11\pi }{12}\]


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