Manipal Engineering Manipal Engineering Solved Paper-2012

  • question_answer
    If\[\underset{x\to \infty }{\mathop{\lim }}\,\left( \frac{{{x}^{3}}+1}{{{x}^{2}}+1}-(ax+b) \right)=2\], then

    A) \[a=1,\,\,b=1\]                 

    B) \[a=1,\,\,b=2\]

    C) \[a=1,\,\,b=-2\]               

    D)         None of these

    Correct Answer: C

    Solution :

    \[\underset{x\to \infty }{\mathop{\lim }}\,\left( \frac{{{x}^{3}}+1}{{{x}^{2}}+1}-(ax+b) \right)=2\] \[\Rightarrow \]               \[\underset{x\to \infty }{\mathop{\lim }}\,\frac{{{x}^{3}}(1-a)-b{{x}^{2}}-ax+(1-b)}{{{x}^{2}}+1}=2\] \[\Rightarrow \]               \[\underset{x\to \infty }{\mathop{\lim }}\,\frac{x(1-a)-b-\frac{a}{x}+\frac{1-b}{{{x}^{2}}}}{1+\frac{1}{{{x}^{2}}}}=b\] \[\Rightarrow \]               \[1-a=0\]    and    \[-b=2\] \[\Rightarrow \]               \[a=1\]          and      \[b=-2\]


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