JEE Main & Advanced Mathematics Differentiation Question Bank Self Evaluation Test - Limits and Derivatives

  • question_answer
    If \[f(x)=\left\{ \begin{matrix}    \frac{{{[x]}^{2}}+\sin [x]}{[x]}for[x]\ne 0  \\    0for[x]=0  \\ \end{matrix} \right.\], where [x] denotes the greatest integer less than or equal to\[x,\] Then \[\underset{x\to 0}{\mathop{\lim }}\,f(x)\] equals

    A) 1

    B) 0

    C) -1

    D) None of these

    Correct Answer: D

    Solution :

    [d] As \[x\to 0-\](i.e., approaches 0 from the left), \[[x]=-1.\] \[\therefore \underset{x\to {{0}^{-}}}{\mathop{\lim }}\,f(x)=\underset{x\to {{0}^{-}}}{\mathop{\lim }}\,\frac{1+\sin (-1)}{-1}=-1+\sin \,\,1\] Whereas, if \[x\to {{0}^{+}}\]we get \[[x]=0.\] \[\therefore f(x)=0\Rightarrow \underset{x\to {{0}^{+}}}{\mathop{\lim }}\,f(x)=0\] Thus, \[\underset{x\to 0}{\mathop{\lim }}\,f(x)\]does not exist.


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