JEE Main & Advanced Mathematics Functions Question Bank Functions

  • question_answer
    Suppose that \[g(x)=1+\sqrt{x}\] and \[f(g(x))=3+2\sqrt{x}+x\], then \[f(x)\] is [MP PET 2000; Karnataka CET 2002]

    A)                    \[1+2{{x}^{2}}\]

    B)            \[2+{{x}^{2}}\]

    C)                    \[1+x\]

    D)            \[2+x\]

    Correct Answer: B

    Solution :

               \[g(x)=1+\sqrt{x}\] and \[f(g(x))=3+2\sqrt{x}+x\] .....(i)            Þ \[f(1+\sqrt{x})=3+2\sqrt{x}+x\]            Put \[1+\sqrt{x}=y\] Þ \[x={{(y-1)}^{2}}\]            then, \[f(y)=3+2(y-1)+{{(y-1)}^{2}}\]\[=2+{{y}^{2}}\]            therefore, \[f(x)=2+{{x}^{2}}\].


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