MCQ
$\mathop {\lim }\limits_{x \to 0} \,x^2(1+2+3+...+[\frac{1}{|x|}])$ is equal to

(where [.] denotes greatest integer function)

  • A
    $0$
  • $\frac{1}{2}$
  • C
    $2$
  • D
    does not exist

Answer

Correct option: B.
$\frac{1}{2}$
b
Put $x=\frac{1}{t}$

$\therefore $ Given limit $ = \mathop {\lim }\limits_{t \to \infty } \frac{{1 + 2 + 3 + .... + \left[ {\left| t \right|} \right]}}{{{t^2}}}$

$ = \mathop {\lim }\limits_{t \to \infty } \frac{{[|t|]([|t|] + 1)}}{{2{t^2}}} = \frac{1}{2}$

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