JEE Main & Advanced Mathematics Functions Question Bank Limits

  • question_answer
    The value of \[\underset{x\to \infty }{\mathop{\lim }}\,\sqrt{{{a}^{2}}{{x}^{2}}+ax+1}-\sqrt{{{a}^{2}}{{x}^{2}}+1}\]is

    A)                 \[\frac{1}{2}\]

    B)                 1

    C)                 \[2\]

    D)                 None of these

    Correct Answer: A

    Solution :

                       \[\underset{x\to \infty }{\mathop{\lim }}\,\,\sqrt{{{a}^{2}}{{x}^{2}}+ax+1}-\sqrt{{{a}^{2}}{{x}^{2}}+1}\]            \[=\underset{x\to \infty }{\mathop{\lim }}\,\,\frac{ax}{\,\sqrt{{{a}^{2}}{{x}^{2}}+ax+1}+\sqrt{{{a}^{2}}{{x}^{2}}+1}}\]                                 \[=\underset{x\to \infty }{\mathop{\lim }}\,\,\frac{a}{\,\sqrt{{{a}^{2}}+\frac{a}{x}+\frac{1}{{{x}^{2}}}}+\sqrt{{{a}^{2}}+\frac{1}{{{x}^{2}}}}}=\frac{a}{2a}=\frac{1}{2}\].


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