MCQ
$\int_0^1 {\frac{{{x^7}}}{{\sqrt {1 - {x^4}} }}dx} $ is equal to
  • A
    $1$
  • $\frac{1}{3}$
  • C
    $\frac{2}{3}$
  • D
    $\frac{\pi }{3}$

Answer

Correct option: B.
$\frac{1}{3}$
b
(b) $I = \int_0^1 {\frac{{{x^7}}}{{\sqrt {1 - {x^4}} }}dx = \int_0^1 {\frac{{{x^6}x\,dx}}{{\sqrt {1 - {x^4}} }}} } $

Put ${x^2} = \sin \theta $ $ \Rightarrow 2x\,dx = \cos \theta \,d\theta $

$I = \frac{1}{2}\int_0^{\pi /2} {\frac{{{{\sin }^3}\theta .\cos \theta \,\,d\theta }}{{\cos \theta }}} $

$= \frac{1}{2}\int_0^{\pi /2} {{{\sin }^3}\theta \,\,d\theta } $

$ = \frac{1}{2}\frac{{\Gamma 2\,\Gamma (1/2)}}{{2.\Gamma (5/2)}} $

$= \frac{{\Gamma \left( {\frac{1}{2}} \right)}}{{4.\frac{3}{2}.\frac{1}{2}.\Gamma \left( {\frac{1}{2}} \right)}} = \frac{1}{3}$.

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