MCQ
$\int_{}^{} {\frac{{1 - \tan x}}{{1 + \tan x}}\;dx = } $
  • A
    $\log \sec \left( {\frac{\pi }{4} - x} \right) + c$
  • B
    $\log \cos \left( {\frac{\pi }{4} + x} \right) + c$
  • $\log \sin \left( {\frac{\pi }{4} + x} \right) + c$
  • D
    None of these

Answer

Correct option: C.
$\log \sin \left( {\frac{\pi }{4} + x} \right) + c$
c
(c)$\int_{}^{} {\frac{{1 - \tan x}}{{1 + \tan x}}\,dx} = \int_{}^{} {\tan \left( {\frac{\pi }{4} - x} \right)} \,dx$
$ = \int_{}^{} {\frac{{\sin \left( {\frac{\pi }{4} - x} \right)}}{{\cos \left( {\frac{\pi }{4} - x} \right)}}} \,dx = \log \cos \left( {\frac{\pi }{4} - x} \right) + c$
$ = \log \sin \left( {\frac{\pi }{4} + x} \right) + c$.

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