JEE Main & Advanced Mathematics Limits, Continuity and Differentiability Question Bank Self Evaluation Test - Continuity and Differentiability

  • question_answer
    Let \[f'(x)=-1+\left| x-2 \right|,\] and \[g(x)=1-\left| x \right|;\] then the set of all points where fog is discontinuous is:

    A) {0, 2}

    B) {0, 1, 2}

    C) {0}

    D) An empty set

    Correct Answer: D

    Solution :

    [d] \[f(g)(x))=f(1-\left| x \right|)=-1+\left| \left| x \right|+1 \right|\] Let \[fog=y\] \[\therefore \,y=-1+\left| \left| x \right|+1 \right|\Rightarrow y=\left\{ \begin{matrix}    x, & x\ge 0  \\    -x, & x<0  \\ \end{matrix} \right.\] LHL at \[(x=0)=\underset{x\to 0}{\mathop{\lim }}\,(-x)=0\] RHL at \[(x=0)=\underset{x\to 0}{\mathop{\lim }}\,(x)=0\] When \[x=0\], then \[y=0\] Hence, LHL at (x = 0)=RHL at (x = 0)= value of y at (x = 0) Hence y is continuous at x = 0 Clearly at all other point y continuous. Therefore, the set of all points where fog is discontinuous is an empty set.


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