JCECE Engineering JCECE Engineering Solved Paper-2008

  • question_answer
    The value of\[\underset{x\to \infty }{\mathop{\lim }}\,\left( \frac{{{x}^{2}}+bx+4}{{{x}^{2}}+ax+5} \right)\]is

    A) \[\frac{b}{a}\]                                  

    B) \[0\]

    C) \[1\]                                     

    D) \[\frac{4}{5}\]

    Correct Answer: C

    Solution :

    \[\underset{x\to \infty }{\mathop{\lim }}\,\frac{{{x}^{2}}+bx+4}{{{x}^{2}}+ax+5}\]                 \[=\underset{x\to \infty }{\mathop{\lim }}\,\frac{\left( 1+\frac{b}{x}+\frac{4}{{{x}^{2}}} \right){{x}^{2}}}{\left( 1+\frac{a}{x}+\frac{5}{{{x}^{2}}} \right){{x}^{2}}}\] Alternative\[\underset{x\to \infty }{\mathop{\lim }}\,\frac{{{x}^{2}}+bx+4}{{{x}^{2}}+ax+5}\]                 \[=\underset{x\to \infty }{\mathop{\lim }}\,\frac{2x+b}{2x+a}\](using\[L'\]Hospital?s rule)                 \[=\underset{x\to \infty }{\mathop{\lim }}\,\frac{2}{2}\]                 \[=1\]


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