JEE Main & Advanced Mathematics Functions Question Bank Functions

  • question_answer
    . Domain of the function \[f(x)={{\left[ {{\log }_{10}}\left( \frac{5x-{{x}^{2}}}{4} \right) \right]}^{1/2}}\] is [UPSEAT 2001]

    A)            \[-\infty <x<\infty \]

    B)            \[1\le x\le 4\]

    C)            \[4\le x\le 16\]

    D)            \[-1\le x\le 1\]

    Correct Answer: B

    Solution :

               We have \[f(x)={{\left[ {{\log }_{10}}\left( \frac{5x-{{x}^{2}}}{4} \right) \right]}^{1/2}}\]     ?..(i)            From (i), clearly \[f(x)\] is defined for those values of x for which \[{{\log }_{10}}\left[ \frac{5x-{{x}^{2}}}{4} \right]\ge 0\]            Þ \[\left( \frac{5x-{{x}^{2}}}{4} \right)\ge {{10}^{0}}\Rightarrow \left( \frac{5x-{{x}^{2}}}{4} \right)\ge 1\]            Þ \[{{x}^{2}}-5x+4\le 0\] Þ \[(x-1)(x-4)\le 0\]                    Hence domain of the function is [1, 4].


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