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

  • question_answer
    \[f(x)=\left\{ \begin{matrix}    \frac{x}{2{{x}^{2}}+\left| x \right|,}\,\,x\ne 0  \\    1.\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,x=0  \\ \end{matrix} \right.\]. Then \[f(x)\] is

    A) continuous but non-differentiable at x=0

    B) differentiable at x=0

    C) discontinuous at x=0

    D) none of these

    Correct Answer: C

    Solution :

    [c] \[f(0+0)=\underset{h\to 0}{\mathop{\lim }}\,f(h)=\underset{h\to 0}{\mathop{\lim }}\,\frac{h}{2{{h}^{2}}+h}=\underset{h\to 0}{\mathop{\lim }}\,\frac{1}{2h+1}=1\] And \[f(0-0)=\underset{h\to 0}{\mathop{\lim }}\,f(-h)=\underset{h\to 0}{\mathop{\lim }}\,\frac{-h}{2{{h}^{2}}+\left| -h \right|}\] \[=\underset{h\to 0}{\mathop{\lim }}\,\frac{-h}{2{{h}^{2}}+h}=\underset{h\to 0}{\mathop{\lim }}\,\frac{-1}{2h+1}=-1\]


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