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

  • question_answer
    \[\frac{d}{dx}\left( {{x}^{2}}\sin \frac{1}{x} \right)=\]

    A)            \[\cos \,\left( \frac{1}{x} \right)+2x\sin \left( \frac{1}{x} \right)\]

    B)            \[2x\sin \left( \frac{1}{x} \right)-\cos \left( \frac{1}{x} \right)\]

    C)            \[\cos \left( \frac{1}{x} \right)-2x\sin \left( \frac{1}{x} \right)\]

    D)            None of these

    Correct Answer: B

    Solution :

               \[\frac{d}{dx}\left( {{x}^{2}}\sin \frac{1}{x} \right)={{x}^{2}}\cos \left( \frac{1}{x} \right)\frac{d}{dx}\left( \frac{1}{x} \right)\]\[+2x\sin \left( \frac{1}{x} \right)\]            \[=-\frac{1}{{{x}^{2}}}.{{x}^{2}}\cos \left( \frac{1}{x} \right)+2x\sin \left( \frac{1}{x} \right)=2x\sin \left( \frac{1}{x} \right)-\cos \left( \frac{1}{x} \right)\].


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