Manipal Engineering Manipal Engineering Solved Paper-2012

  • question_answer
    lf\[f(x)=\left\{ \begin{matrix}    \frac{\sin [x]}{[x]}, & [x]\ne 0  \\    0, & [x]=0  \\ \end{matrix} \right.\] 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 :

    As,          \[f(x)=\left\{ \begin{matrix}    \frac{\sin [x]}{[x]}m & [x]\ne 0  \\    0, & [x]=0  \\ \end{matrix} \right.\] \[\Rightarrow \]               \[f(x)=\left\{ \begin{matrix}    \frac{\sin [x]}{[x]}, & x\in R-[0,\,\,1)  \\    0, & 0\le x<1  \\ \end{matrix} \right.\] \[\therefore \]  \[RHL\]at\[x=0\]                 \[\underset{x\to {{0}^{+}}}{\mathop{\lim }}\,f(x)=\underset{x\to 0}{\mathop{\lim }}\,\frac{\sin [0+h]}{[0+h]}=0\]                 \[LHL\]at\[x=0\]                 \[\underset{x\to {{0}^{-}}}{\mathop{\lim }}\,f(x)=\underset{h\to 0}{\mathop{\lim }}\,\frac{\sin [0-h]}{[0-h]}\]                                   \[=\underset{h\to 0}{\mathop{\lim }}\,\frac{\sin (-1)}{-1}=\sin 1\] Since,           \[RHL\ne LHL\] \[\therefore \]Limit does not exist.


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