MCQ
$\int {\frac{{\cos 2x - 1\,\,}}{{\cos 2x + 1}}dx = } $
  • A
    $\tan x - x + c$
  • B
    $x + \tan x + c$
  • $x - \tan x + c$
  • D
    $ - x - \cot x + c$

Answer

Correct option: C.
$x - \tan x + c$
c
(c)$\int {\frac{{\cos 2x - 1}}{{\cos 2x + 1}}\,} dx$
$ \Rightarrow \,I = - \int {\frac{{(1 - \cos 2x)}}{{(1 + \cos 2x)}}} \,dx$$ = - \int {\frac{{2{{\sin }^2}x}}{{2{{\cos }^2}x}}\,dx} $
$ \Rightarrow I = - \int {{{\tan }^2}x\,dx} $$ = - \int {({{\sec }^2}x - 1)\,dx} $
$ \Rightarrow I = - \int {{{\sec }^2}x\,dx + \int {1\,dx} } $$ = - \tan x + x + c$
==> $I = x - \tan x + c$

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