MCQ
The value of $\int_0^{\pi /2} {\frac{{dx}}{{1 + {{\tan }^3}x}}} $ is
  • A
    $0$
  • B
    $1$
  • C
    $\frac{\pi }{2}$
  • $\frac{\pi }{4}$

Answer

Correct option: D.
$\frac{\pi }{4}$
d
(d) $I = \int_0^{\pi /2} {\frac{{dx}}{{1 + {{\tan }^3}x}} = \int_0^{\pi /2} {\frac{{{{\cos }^3}x}}{{{{\sin }^3}x + \cos {x^3}}}} } dx$ ....$(i)$

$ = \int_0^{\pi /2} {\frac{{{{\sin }^3}x}}{{{{\cos }^3}x + {{\sin }^3}x}}dx} $ .....$(ii)$

Adding $(i)$ and $(ii),$ we get 

$2I = \int_0^{\pi /2} {dx \Rightarrow I = \frac{\pi }{4}.} $

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