MCQ
$\tan ^{-1}\left(\frac{\sqrt{1+x^2}-1}{x}\right)=$
  • A
    $\tan ^{-1} x$
  • $\frac{1}{2} \tan ^{-1} x$
  • C
    $2 \tan ^{-1} x$
  • D
    $3 \tan ^{-1} x$

Answer

Correct option: B.
$\frac{1}{2} \tan ^{-1} x$
(B) $\tan ^{-1}\left(\frac{\sqrt{1+x^2}-1}{x}\right)$
$=\tan ^{-1}\left[\frac{\sqrt{1+\tan ^2 \theta}-1}{\tan \theta}\right]$
(Putting $x=\tan \theta$ )
$=\tan ^{-1}\left[\frac{\sec \theta-1}{\tan \theta}\right]=\tan ^{-1}\left[\frac{1-\cos \theta}{\sin \theta}\right]$
$=\tan ^{-1}\left[\frac{2 \sin ^2 \frac{\theta}{2}}{2 \sin \frac{\theta}{2} \cos \frac{\theta}{2}}\right]$
$=\tan ^{-1}\left(\tan \frac{\theta}{2}\right)$
$=\frac{\theta}{2}=\frac{1}{2} \tan ^{-1} x$

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