MCQ
$\int_0^{\pi /2} {\frac{{\cos x}}{{1 + \cos x + \sin x}}} \,dx = $
  • A
    $\frac{\pi }{4} + \frac{1}{2}\log 2$
  • B
    $\frac{\pi }{4} + \log 2$
  • $\frac{\pi }{4} - \frac{1}{2}\log 2$
  • D
    $\frac{\pi }{4} - \log 2$

Answer

Correct option: C.
$\frac{\pi }{4} - \frac{1}{2}\log 2$
c
(c) $\int_0^{\pi /2} {\frac{{\cos x}}{{1 + \cos x + \sin x}}} dx$

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

$ = \frac{1}{2}\int_0^{\pi /2} {\frac{{1 - {{\tan }^2}(x/2)}}{{1 + \tan (x/2)}}} dx = \frac{1}{2}\int_0^{\pi /2} {\left[ {1 - \tan \left( {\frac{x}{2}} \right)} \right]} dx$

$\frac{\pi }{4} + \log \frac{1}{{\sqrt 2 }} = \frac{\pi }{4} - \frac{1}{2}\log 2$

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