JEE Main & Advanced JEE Main Paper (Held On 9 April 2016)

  • question_answer
    If\[\underset{x\to \infty }{\mathop{Lim}}\,{{\left( 1+\frac{a}{x}-\frac{4}{{{x}^{2}}} \right)}^{2x}}={{e}^{3}},\]then ?a? is equal to:   JEE Main Online Paper (Held On 09 April 2016)

    A) \[\frac{2}{3}\]                                   

    B) \[\frac{3}{2}\]

    C) 2                                             

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

    Correct Answer: B

    Solution :

                    \[L=\underset{x\to \infty }{\mathop{Lim}}\,{{\left( 1+\frac{a}{x}-\frac{4}{{{x}^{2}}} \right)}^{2x}}\]must be of the from \[{{1}^{\infty }}\] \[L={{e}^{\underset{x\to \infty }{\mathop{lim}}\,\left( \frac{a}{x}-\frac{4}{{{x}^{2}}} \right)2x}}\]\[\Rightarrow \]\[L={{e}^{\underset{x\to \infty }{\mathop{lim}}\,\left( \frac{ax-4}{x} \right)}}\] \[={{e}^{2a}}={{e}^{3}}\]                                              \[a=\frac{3}{2}\]


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