MCQ
$\mathop {\lim }\limits_{x \to a} \frac{{\sqrt {a + 2x} - \sqrt {3x} }}{{\sqrt {3a + x} - 2\sqrt x }} = $$(a \ne 0)$
  • A
    $\frac{1}{{\sqrt 3 }}$
  • $\frac{2}{{3\sqrt 3 }}$
  • C
    $\frac{2}{{\sqrt 3 }}$
  • D
    $\frac{2}{3}$

Answer

Correct option: B.
$\frac{2}{{3\sqrt 3 }}$
b
(b) $\mathop {\lim }\limits_{x \to a} \,\frac{{\sqrt {a + 2x} - \sqrt {3x} }}{{\sqrt {3a + x} - 2\sqrt x }}$

$ = \mathop {\lim }\limits_{x \to a} \,\frac{{\sqrt {a + 2x} - \sqrt {3x} }}{{\sqrt {3a + x} - 2\sqrt x }} \times \frac{{\sqrt {a + 2x} + \sqrt {3x} }}{{\sqrt {a + 2x} + \sqrt {3x} }} \times \frac{{\sqrt {3a + x} + 2\sqrt x }}{{\sqrt {3a + x} + 2\sqrt x }}$

$ = \mathop {\lim }\limits_{x \to a} \frac{{\sqrt {3a + x} + 2\sqrt x }}{{3\,(\sqrt {a + 2x} + \sqrt {3x)} }} = \frac{2}{{3\sqrt 3 }}$.

Aliter : Apply $L-$ Hospital’s rule.

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