MCQ
Choose the correct answer from the given four options. If $3\tan^{-1}\text{x}+\cot^{-1}\text{x}=\pi,$ then $x$ equals:
  • A
    $0$
  • $1$
  • C
    $-1$
  • D
    $\frac{1}{2}$

Answer

Correct option: B.
$1$
We have, $3\tan^{-1}\text{x}+\cot^{-1}\text{x}=\pi$
$\Rightarrow 2\tan^{-1}\text{x}+(\tan^{-1}\text{x}+\cot^{-1}\text{x})=\pi$
$\Rightarrow 2\tan^{-1}\text{x}+\frac{\pi}{2}=\pi$
$\Big(\because \tan^{-1}\text{x}+\cot^{-1}\text{x}=\frac{\pi}{2}\Big)$
$\Rightarrow 2\tan^{-1}\text{x}=\frac{\pi}{2}$
$\Rightarrow \tan^{-1}\text{x}=\frac{\pi}{4}$
$\Rightarrow \text{x}=1$

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