JEE Main & Advanced Mathematics Functions Question Bank Continuity

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

    A)            \[f:R\to R\]is continuous at \[x=0\]

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

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

    D)            None of these

    Correct Answer: B

    Solution :

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