MCQ
$\tan ^{-1} 3+\tan ^{-1} \lambda=\tan ^{-1}\left(\frac{3+\lambda}{1-3 \lambda}\right)$ is valid for what values of $\lambda ?$
  • A
    $\lambda \in\left(-\frac{1}{3}, \frac{1}{3}\right)$
  • B
    $\lambda > \frac{1}{3}$
  • $\lambda < \frac{1}{3}$
  • D
    All real values of $\lambda$

Answer

Correct option: C.
$\lambda < \frac{1}{3}$
$\text {Given, } \tan ^{-1} 3+\tan ^{-1} \lambda$
$=\tan ^{-1}\left(\frac{3+\lambda}{1-3 \lambda}\right)$
$\tan ^{-1} 3+\tan ^{-1} \lambda$
$=\tan ^{-1}\left(\frac{3+\lambda}{1-3 \lambda}\right) \text { for } 3 \lambda < 1$
$\therefore 3 \lambda < 1$
$\Rightarrow \lambda < \frac{1}{3}$

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