JEE Main & Advanced Mathematics Functions Question Bank Continuity

  • question_answer
    If \[f(x)=\left\{ \begin{align}   & ({{x}^{2}}/a)-a,\ \ \text{when}\ x<a \\  & \ \ \ \ \ \ \ \ \ \ \ 0,\ \ \text{when}\ x=a\text{,} \\  & a-({{x}^{2}}/a),\ \ \text{when }x>a \\ \end{align} \right.\] then

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

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

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

    D)            None of these

    Correct Answer: B

    Solution :

               \[f(a)=0\]                    \[\underset{x\to a-}{\mathop{\lim }}\,\,f(x)=\underset{x\to a-}{\mathop{\lim }}\,\left( \frac{{{x}^{2}}}{a}-a \right)=\underset{h\to 0}{\mathop{\lim }}\,\,\left\{ \frac{{{(a-h)}^{2}}}{a}-a \right\}=0\]                    and \[\underset{x\to a+}{\mathop{\lim }}\,f(x)=\underset{h\to 0}{\mathop{\lim }}\,\,\,\left\{ a-\frac{{{(a+h)}^{2}}}{a} \right\}=0\]            Hence it is continuous at \[x=a\].


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