JEE Main & Advanced Mathematics Differentiation Question Bank Derivative at a point Standard Differentiation

  • question_answer
    \[\frac{d}{dx}\,\,\left[ {{\tan }^{-1}}\left( \frac{\sqrt{x}(3-x)}{1-3x} \right) \right]\]=                                                [Kerala (Engg.) 2005]

    A)            \[\frac{1}{2(1+x)\,\sqrt{x}}\]

    B)            \[\frac{3}{(1+x)\,\sqrt{x}}\]

    C)            \[\frac{2}{(1+x)\,\sqrt{x}}\]

    D)            \[\frac{2\sqrt{2}y-3}{2\sqrt{2}}=\frac{-3\sqrt{2}\times +3}{2\sqrt{2}}\]

    E)            \[\frac{3}{2(1+x)\sqrt{x}}\]

    Correct Answer: E

    Solution :

               \[\frac{d}{dx}\,\left( {{\tan }^{-1}}\frac{(\sqrt{x}(3-x)}{1-3x} \right)\]                    Put \[\sqrt{x}=\tan \theta \Rightarrow \theta ={{\tan }^{-1}}\sqrt{x}\]                    \[\frac{d}{dx}\left( {{\tan }^{-1}}\frac{(\tan \theta (3-{{\tan }^{2}}\theta )}{1-3{{\tan }^{2}}\theta } \right)\]                    \[\frac{d}{dx}\left( {{\tan }^{-1}}\frac{(3\tan \theta -{{\tan }^{3}}\theta )}{1-3{{\tan }^{2}}\theta } \right)\]                    \[\frac{d}{dx}({{\tan }^{-1}}(\tan 3\theta )=\frac{d}{dx}(3\theta )\]                    \[\frac{d}{dx}(3.{{\tan }^{-1}}\sqrt{x})=\frac{3}{2\sqrt{x}(1+x)}\].


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