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

  • question_answer
    The derivative of \[{{\tan }^{-1}}\left( \frac{\sin x-\cos x}{\sin x+\cos x} \right),\]with respect to \[\frac{x}{2},\]where \[\left( x\in \left( 0,\frac{\pi }{2} \right) \right)\]is : [JEE Main 12-4-2019 Afternoon]

    A) \[\frac{1}{2}\]                        

    B) \[\frac{2}{3}\]

    C) \[1\]                 

    D) \[2\]

    Correct Answer: D

    Solution :

    \[f\left( x \right)={{\tan }^{-1}}\left( \frac{\sin x-\cos x}{\sin x+\cos x} \right)\]           \[={{\tan }^{-1}}\left( \frac{\tan x-1}{\tan x+1} \right)={{\tan }^{-1}}\left( \tan \left( x-\frac{\pi }{4} \right) \right)\]           \[\because \]\[=x-\frac{\pi }{4}\in \left( -\frac{\pi }{4},\frac{\pi }{4} \right)\]           \[\therefore \]\[=f\left( x \right)=x-\frac{\pi }{4}\] \[\Rightarrow \]its derivative w.r.t. \[\frac{x}{2}\] is \[\frac{1}{1/2}=2\]


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