JEE Main & Advanced Mathematics Functions Question Bank Limits

  • question_answer
    Let the function f be defined by the equation \[f(x)=\left\{ \begin{align}   & 3x\ \ \ \ \ \ \text{if}\ 0\le x\le 1 \\  & 5-3x\ \ \text{if}\ \text{1}<x\le 2 \\ \end{align} \right.,\]then [SCRA 1996]

    A)                 \[\underset{x\to 1}{\mathop{\lim }}\,f(x)=f(1)\]

    B)                 \[\underset{x\to 1}{\mathop{\lim }}\,f(x)=3\]

    C)                 \[\underset{x\to 1}{\mathop{\lim }}\,f(x)=2\]

    D)                 \[\underset{x\to 1}{\mathop{\lim }}\,f(x)\]does not exist

    Correct Answer: D

    Solution :

                       L.H.L.\[=\underset{x\to 1-0}{\mathop{\lim }}\,f(x)=\underset{h\to 0}{\mathop{\lim }}\,\,\,(1-h)=\underset{h\to 0}{\mathop{\lim }}\,\,\,3(1-h)\]                      \[=\underset{h\to 0}{\mathop{\lim }}\,\,\,(3-3h)=3-3\,.\,0=3\]            R.H.L.\[=\underset{x\to 1+0}{\mathop{\lim }}\,f(x)=\underset{h\to 0}{\mathop{\lim \,\,}}\,\,f\,(1+h)=\underset{h\to 0}{\mathop{\lim }}\,\,\,[5-3(1+h)]\]                  \[=\underset{h\to 0}{\mathop{\lim }}\,\,\,(2-3h)=2-3\,.\,0=2\]                 Hence \[\underset{x\to 1}{\mathop{\lim }}\,\,\,f(x)\] does not exist.


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