JEE Main & Advanced Mathematics Functions Question Bank Differentiability

  • question_answer
    The function \[f(x)=|x|\] at \[x=0\] is [MP PET 1993]

    A)            Continuous but non-differentiable

    B)            Discontinuous and differentiable

    C)            Discontinuous and non-differentiable

    D)            Continuous and differentiable

    Correct Answer: A

    Solution :

               Since this function is continuous at \[x=0\]            Now for differentiability            \[f(x)=\,|\,\,x\,\,|\,\,=\,\,|0|\,\,=0\] and \[f(0+h)=f(h)=\,\,|h|\]            \[\therefore \,\,\underset{h\to 0-}{\mathop{\lim }}\,\,\frac{f(0+h)-f(0)}{h}=\underset{h\to 0-}{\mathop{\lim }}\,\,\frac{|h|}{h}=-1\]            and \[\underset{h\to 0+}{\mathop{\lim }}\,\,\frac{f(0+h)-f(0)}{h}=\underset{h\to 0+}{\mathop{\lim }}\,\,\frac{|h|}{h}=1\].                    Therefore it is continuous and non-differentiable.


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