JEE Main & Advanced Mathematics Functions Question Bank Limits

  • question_answer
    The value of \[\underset{x\to -\infty }{\mathop{\lim }}\,\frac{\sqrt{4{{x}^{2}}+5x+8}}{4x+5}\]is [Roorkee 1998]

    A)                 \[-1/2\]

    B)                 0

    C)                 \[1/2\]

    D)                 1

    Correct Answer: A

    Solution :

                       \[\underset{x\,\to \,-\infty }{\mathop{\lim }}\,\,\frac{\sqrt{4{{x}^{2}}+5x+8}}{4x+5}\]\[=\underset{h\to 0}{\mathop{\lim }}\,\,\,\frac{\sqrt{4\,{{(-1/h)}^{2}}+5\,(-1/h)+8}}{4\,(-1/h)+5}\]                                                 \[=\underset{h\to 0}{\mathop{\lim }}\,\,\,\frac{(1/h)\sqrt{4\,-5h+8{{h}^{2}}}}{(1/h)\,(-\,4+5h)}=\frac{\sqrt{4}}{-4}=-\frac{1}{2}\].


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