JEE Main & Advanced Mathematics Functions Question Bank Self Evaluation Test - Relation and Functions-II

  • question_answer
    If \[f(x)=2x+\left| x \right|,g(x)=\frac{1}{3}(2x-\left| x \right|)\] and \[h(x)=f(g(x)),\] then domain of \[{{\sin }^{-1}}\]\[\underbrace{(h(h(h(h...h(x)...))))}_{n\,times}\] is

    A) \[[-1,1]\]

    B) \[\left[ -1,-\frac{1}{2} \right]\cup \left[ \frac{1}{2},1 \right]\]

    C) \[\left[ -1,-\frac{1}{2} \right]\]

    D) \[\left[ \frac{1}{2},1 \right]\]

    Correct Answer: A

    Solution :

    [a] Since, f(x)= \[\left\{ \begin{matrix}    2x+x.x\ge 0  \\    2x-x,x<0  \\ \end{matrix}=\left\{ \begin{matrix}    3x,x\ge 0  \\    x,x<0  \\ \end{matrix} \right. \right.\] and \[g(x)=\frac{1}{3}\left\{ \begin{matrix}    2x-x,x\ge 0  \\    2x+x,x<0  \\ \end{matrix} \right.=\left\{ \begin{matrix}    \frac{x}{3},x\ge 0  \\    x,x<0  \\ \end{matrix} \right.\] \[\therefore f(g(x))=\left\{ \begin{matrix}    3\left( \frac{x}{3} \right),x\ge 0  \\    x,x<0  \\ \end{matrix} \right.\] \[\therefore f(g(x))=x\forall x\in R\therefore h(x)=x\] \[\Rightarrow {{\sin }^{-1}}(h(h(h...(h(x)..)))=si{{n}^{-1}}x\] Thus, domain of \[{{\sin }^{-1}}(h(h(h(h..h(x)...))))is[-1,1].\]


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