Considering only the principal values of an inverse function, the set $\mathrm{A}=\left\{x \geq 0 / \tan…

Considering only the principal values of an inverse function, the set $\mathrm{A}=\left\{x \geq 0 / \tan ^{-1} x+\tan ^{-1} 6 x=\frac{\pi}{4}\right\}$
  1. is an empty set.
  2. is a singleton set.
  3. contains more than two elements.
  4. contains two elements.

Solution

Consider, $\tan ^{-1} x+\tan ^{-1} 6 x=\frac{\pi}{4}$ $\begin{aligned} & \Rightarrow \tan ^{-1}\left(\frac{7 x}{1-6 x^2}\right)=\frac{\pi}{4} \\ & \quad \quad \ldots\left[\tan ^{-1}(x)+\tan ^{-1}(y)=\tan ^{-1}\left(\frac{x+y}{1-x y}\right)\right] \\ & \Rightarrow \frac{7 x}{1-6 x^2}=1 \\ & \Rightarrow 7 x=1-6 x^2 \\ & \Rightarrow 6 x^2+7 x-1=0 \\ & \Rightarrow x=\frac{-7 \pm \sqrt{73}}{12} \\ & \quad \text { Since } x \geq 0 \\ & \therefore \quad x=\frac{-7+\sqrt{73}}{12} \end{aligned}$ $\therefore \quad$ A is a singleton set.

Asked in: MHT CET 2023 (10 May Shift 1)

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