JEE Main & Advanced Mathematics Differentiation Question Bank Differentiation by Substitution

  • question_answer
    The derivative of \[{{\cos }^{-1}}\left( \frac{1-{{x}^{2}}}{1+{{x}^{2}}} \right)\] w.r.t. \[{{\cot }^{-1}}\left( \frac{1-3{{x}^{2}}}{3x-{{x}^{2}}} \right)\] is                                                               [Karnataka CET 2003]

    A)            1

    B)            \[\frac{3}{2}\]

    C)            \[\frac{2}{3}\]

    D)            \[\frac{1}{2}\]

    Correct Answer: C

    Solution :

               Let \[{{y}_{1}}={{\cos }^{-1}}\left( \frac{1-{{x}^{2}}}{1+{{x}^{2}}} \right)\,\,\,=2{{\tan }^{-1}}x\],            \[{{\cot }^{-1}}\left( \frac{1-3{{x}^{2}}}{3x-{{x}^{3}}} \right)=3{{\tan }^{-1}}x\Rightarrow \frac{d{{y}_{1}}}{d{{y}_{2}}}=\frac{\left( \frac{d{{y}_{1}}}{dx} \right)}{\left( \frac{d{{y}_{2}}}{dx} \right)}=\frac{\left( \frac{2}{1+{{x}^{2}}} \right)}{\left( \frac{3}{1+{{x}^{2}}} \right)}=\frac{2}{3}\]


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