MCQ
$\mathop {\lim }\limits_{x \to 1} \frac{{1 - \sqrt x }}{{{{({{\cos }^{ - 1}}x)}^2}}} = $
  • A
    $1$
  • B
    $\frac{1}{2}$
  • $\frac{1}{4}$
  • D
    None of these

Answer

Correct option: C.
$\frac{1}{4}$
c
(c) Put ${\cos ^{ - 1}}x = y$ and $x \to 1\, \Rightarrow \,\,y \to 0.$

$\mathop {\lim }\limits_{x \to 1} \,\frac{{1 - \sqrt x }}{{{{({{\cos }^{ - 1}}x)}^2}}} = \mathop {\lim }\limits_{y \to 0} \,\frac{{1 - \sqrt {\cos y} }}{{{y^2}}}$

Now rationalizing it, we get

$\mathop {\lim }\limits_{y \to 0} \,\frac{{(1 - \cos y)}}{{{y^2}(1 + \sqrt {\cos y} )}}$

$ = \mathop {\lim }\limits_{y \to 0} \,\frac{{1 - \cos y}}{{{y^2}}}\,.\,\mathop {\lim }\limits_{y \to 0} \,\frac{1}{{1 + \sqrt {\cos y} }} $

$= \frac{1}{2} \times \frac{1}{2} = \frac{1}{4}.$

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