JEE Main & Advanced Mathematics Functions Question Bank Self Evaluation Test - Relations and Functions-I

  • question_answer
    Find the domain of \[f(x)=\sqrt{{{(0.625)}^{4-3x}}-{{(1.6)}^{x(x+8)}}}\]

    A) \[[-3,2]\]

    B)        \[[1,4]\]

    C) \[[2,5]\]

    D)        \[[-4,-1]\]

    Correct Answer: D

    Solution :

    [d] Clearly, \[{{(0.625)}^{4-3x}}\ge {{(1.6)}^{x(x+8)}}\] or \[{{\left( \frac{5}{8} \right)}^{4-3x}}\ge {{\left( \frac{8}{5} \right)}^{x(x+8)}}\] or \[{{\left( \frac{8}{5} \right)}^{3x-4}}\ge {{\left( \frac{8}{5} \right)}^{x(x+8)}}\] or \[3x-4\ge {{x}^{2}}+8x\] or \[{{x}^{2}}+5x+4\le 0\] or \[-4\le x\le -1\] Hence, the domain of function \[f(x)\] is \[x\in [-4,-1]\]


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