MCQ
A solution of the equation $\tan ^{-1}(1+x)+\tan ^{-1}(1-x)=\frac{\pi}{2}$ is
  • A
    $x=1$
  • B
    $x=-1$
  • $x=0$
  • D
    $x=\pi$

Answer

Correct option: C.
$x=0$
(C) $\tan ^{-1}(1+x)+\tan ^{-1}(1-x)=\frac{\pi}{2}$
$\Rightarrow \tan ^{-1}(1+x)=\frac{\pi}{2}-\tan ^{-1}(1-x)$
$\Rightarrow \tan ^{-1}(1+x)=\cot ^{-1}(1-x)$
$\Rightarrow \tan ^{-1}(1+x)=\tan ^{-1}\left(\frac{1}{1-x}\right)$
$\Rightarrow 1+x=\frac{1}{1-x} \Rightarrow 1-x^2=1 \Rightarrow x=0$

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