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JEE Main & Advanced Mathematics Functions Question Bank Critical Thinking

  • question_answer
    If \[f:R\to R\]and \[g:R\to R\] are defined by \[f(x)=2x+3\]and \[g(x)={{x}^{2}}+7\], then the values of x such that \[g(f(x))=8\] are [EAMCET 2000, 03]

    A) 1, 2

    B) -1, 2

    C) -1, -2

    D) 1, -2

    Correct Answer: C

    Solution :

    • \[g\left[ f(x) \right]=8\] or \[g(2x+3)=8\]           
    • Þ \[{{(2x+3)}^{2}}+7=8\] Þ \[2x+3=\pm 1\] Þ \[x=-1,\,-2\].


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