MCQ
If $\mathop {\lim }\limits_{x \to \infty } {\left( {1 + \frac{a}{x} - \frac{4}{{{x^2}}}} \right)^{2x}} = {e^3},$ then $'a'$ is equal to
  • A
    $2$
  • $\frac  {3}{2}$
  • C
    $\frac  {1}{2}$
  • D
    $\frac  {2}{3}$

Answer

Correct option: B.
$\frac  {3}{2}$
b
$\,\mathop {\lim }\limits_{x \to \infty } {\left( {1 + \frac{a}{x} - \frac{4}{{{x^2}}}} \right)^{2x}}\,\,\,\,\,\,\,\,\,\left( {{1^{\infty \,}}from} \right)$

$\, = e\left[ {\mathop {\lim }\limits_{x \to \infty } \left( {1 + \frac{a}{x} - \frac{4}{{{x^2}}} - 1} \right)2x} \right]$

        $\, = e\left[ {\mathop {\lim }\limits_{x \to \infty } \left( {1 + \frac{a}{x} - \frac{4}{{{x^2}}} - 1} \right)2x} \right]$

$\therefore 2a = 3 \Rightarrow a = 3/2$

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