JCECE Engineering JCECE Engineering Solved Paper-2014

  • question_answer
    If\[f(x)=\left\{ \begin{matrix}    -{{x}^{2}}, & when\,\,x\le 0  \\    5x-4, & when\,\,0<x\le 1  \\    4{{x}^{2}}-3x, & when\,\,1<x<2  \\    3x+4, & when\,\,x\ge 2  \\ \end{matrix} \right.\]then

    A)  \[f(x)\]is continuous at\[x=0\]

    B)  \[f(x)\]is continuous at\[x=2\]

    C)  \[f(x)\]is discontinuous at\[x=1\]

    D)  None of the above

    Correct Answer: B

    Solution :

    \[\underset{x\to {{0}^{-}}}{\mathop{\lim }}\,f(x)=0\] \[f(0)=0,\,\,\underset{x\to {{0}^{+}}}{\mathop{\lim }}\,f(x)=4\] \[\therefore \]\[f(x)\]is discontinuous at\[x=0\]. and        \[\underset{x\to {{1}^{-}}}{\mathop{\lim }}\,f(x)=1\underset{x\to {{1}^{+}}}{\mathop{\lim }}\,f(x)=1,\,\,f(1)=1\] \[\therefore \]\[f(x)\]is continuous at\[~x=1\]. Also,      \[\underset{x\to {{2}^{-}}}{\mathop{\lim }}\,f(x)=4{{(2)}^{2}}-3(2)=0\]                 \[f(2)=10\] and        \[\underset{x\to {{2}^{+}}}{\mathop{\lim }}\,f(x)=3(2)+4=10\] Hence, \[f(x)\]is continuous at\[x=2\].


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