JEE Main & Advanced Mathematics Limits, Continuity and Differentiability Question Bank Self Evaluation Test - Continuity and Differentiability

  • question_answer
    If f(x) is differentiable everywhere, then which one of the following is correct?

    A) \[\left| f \right|\] is differentiable everywhere

    B) \[{{\left| f \right|}^{2}}\]is differentiable everywhere

    C) \[f\left| f \right|\]is not differentiable at some points

    D) None of the above

    Correct Answer: C

    Solution :

    [c] If f(x) is differential everywhere then |f| is not differentiable at some point, so, \[f\left| \,x \right|\] is not differentiable at some point. [Example: f(x) = x is differentiable everywhere but |f(x)|= |x| is not differentiable at x = 0]


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