MCQ
$\frac{1}{{\sqrt {5 + 4x} }}$ can be expanded by binomial theorem, if
  • A
    $x < 1$
  • B
    $|x| < 1$
  • $|x|\,\, < \frac{5}{4}$
  • D
    $|x| < \frac{4}{5}$

Answer

Correct option: C.
$|x|\,\, < \frac{5}{4}$
c
(c) The given expression can be written as ${5^{ - 1/2}}{\left( {1 + \frac{4}{5}x} \right)^{ - 1/2}}$and it is valid only when

$\left| {\frac{4}{5}x} \right| < 1$

$\Rightarrow |x| < \frac{5}{4}$

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