JEE Main & Advanced Mathematics Functions Question Bank Continuity

  • question_answer
    If \[f(x)=\]\[\left\{ \begin{align}   & \frac{1-(x)}{1+x},\,\,\,\,\,x\ne -1 \\  & \,\,1\,\,\,\,\,\,\,\,\,,\,\,\,\,\,x=-1 \\ \end{align} \right.\], then  the value of \[f(|2k|)\]will be (where [ ] shows the greatest integer function) [DCE 2005]

    A)            Continuous at \[x=-1\]

    B)            Continuous at \[x=0\]

    C)            Discontinuous at \[x=\frac{1}{2}\]

    D)            All of these

    Correct Answer: D

    Solution :

               \[f(x)=\left\{ \begin{align}   & \frac{1-|x|}{1+x},\,x\ne -1 \\  & 1\,\,\,\,\,\,\,\,\,\,\,,\,\,x=-1 \\ \end{align} \right.\] and \[f(x)=\left\{ \begin{align}   & 1\,\,\,\,\,\,\,\,\,,x<0 \\  & \frac{1-x}{1+x}\,,x\ge 0 \\ \end{align} \right.\]                    \[f(2x)=\left\{ \begin{align}   & 1\,\,\,\,\,\,\,\,\,\,\,\,\,,\,\,x<0 \\  & \frac{1-[2x]}{1+[2x]},\,\,x>0 \\ \end{align} \right.\]Þ \[f(2x)=\left\{ \begin{align}   & 1\,\,\,\,\,\,\,\,\,\,,\,\,x<0 \\  & 1\,\,\,\,\,\,\,\,\,\,,\,\,0\le x<\frac{1}{2} \\  & 0\,\,\,\,\,\,\,\,\,\,,\,\,\frac{1}{2}\le x\le 1 \\  & -\frac{1}{3}\,\,\,\,\,,\,\,\,1\le x<\frac{3}{2} \\ \end{align} \right.\]                     Þ \[f(x)\], for all values of x where \[x<\frac{1}{2}\]a continous function and for \[x=\frac{1}{2}\] and \[x=1\] \[f(x)\]be a discontinous  function.


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