MCQ
$\int\limits_0^{\frac{\pi }{2}} {\,\,\frac{{d\,x}}{{{{\cos }^6}x + \,{{\sin }^6}\,x}}}$  is equal to :
  • A
    zero
  • $\pi$
  • C
    $\pi /2$
  • D
    $2 \pi $

Answer

Correct option: B.
$\pi$
b
$I = \int\limits_0^{\frac{\pi }{2}} {\,\,\frac{{d\,x}}{{1\,\, - \,\,3\,{{\sin }^2}\,x\,\,{{\cos }^2}\,x}}}$

 $= \int\limits_0^{\frac{\pi }{2}} {\,\,\frac{{d\,x}}{{1\,\, - \,\,{\textstyle{3 \over 4}}\,{{\sin }^2}\,2x}}}$ 

$= 2 \int\limits_0^\pi  {\,\,\frac{{d\,t}}{{4\,\, - \,\,3\,{{\sin }^2}\,t}}}$

where $2x = t$

$= 4 \, \int\limits_0^{\frac{\pi }{2}} {\,\,\frac{{d\,t}}{{4\,\, - \,\,3\,{{\sin }^2}\,t}}}$ etc.

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